Add bg-cancel action to ignore running background transforms

Close #4430

Example:

  # Implement popup that disappears after 1 second
  #   * Use footer as the popup
  #   * Use `bell` to ring the terminal bell
  #   * Use `bg-transform-footer` to clear the footer after 1 second
  #   * Use `bg-cancel` to ignore currently running background transform actions
  fzf --multi --list-border \
      --bind 'enter:execute-silent(echo -n {+} | pbcopy)+bell' \
      --bind 'enter:+transform-footer(echo Copied {} to clipboard)' \
      --bind 'enter:+bg-cancel+bg-transform-footer(sleep 1)'

src/actiontype_string.go

@@ -128,49 +128,50 @@ func _() {
 	_ = x[actBgTransformPrompt-117]
 	_ = x[actBgTransformQuery-118]
 	_ = x[actBgTransformSearch-119]
-	_ = x[actSearch-120]
-	_ = x[actPreview-121]
-	_ = x[actPreviewTop-122]
-	_ = x[actPreviewBottom-123]
-	_ = x[actPreviewUp-124]
-	_ = x[actPreviewDown-125]
-	_ = x[actPreviewPageUp-126]
-	_ = x[actPreviewPageDown-127]
-	_ = x[actPreviewHalfPageUp-128]
-	_ = x[actPreviewHalfPageDown-129]
-	_ = x[actPrevHistory-130]
-	_ = x[actPrevSelected-131]
-	_ = x[actPrint-132]
-	_ = x[actPut-133]
-	_ = x[actNextHistory-134]
-	_ = x[actNextSelected-135]
-	_ = x[actExecute-136]
-	_ = x[actExecuteSilent-137]
-	_ = x[actExecuteMulti-138]
-	_ = x[actSigStop-139]
-	_ = x[actFirst-140]
-	_ = x[actLast-141]
-	_ = x[actReload-142]
-	_ = x[actReloadSync-143]
-	_ = x[actDisableSearch-144]
-	_ = x[actEnableSearch-145]
-	_ = x[actSelect-146]
-	_ = x[actDeselect-147]
-	_ = x[actUnbind-148]
-	_ = x[actRebind-149]
-	_ = x[actToggleBind-150]
-	_ = x[actBecome-151]
-	_ = x[actShowHeader-152]
-	_ = x[actHideHeader-153]
-	_ = x[actBell-154]
-	_ = x[actExclude-155]
-	_ = x[actExcludeMulti-156]
-	_ = x[actAsync-157]
+	_ = x[actBgCancel-120]
+	_ = x[actSearch-121]
+	_ = x[actPreview-122]
+	_ = x[actPreviewTop-123]
+	_ = x[actPreviewBottom-124]
+	_ = x[actPreviewUp-125]
+	_ = x[actPreviewDown-126]
+	_ = x[actPreviewPageUp-127]
+	_ = x[actPreviewPageDown-128]
+	_ = x[actPreviewHalfPageUp-129]
+	_ = x[actPreviewHalfPageDown-130]
+	_ = x[actPrevHistory-131]
+	_ = x[actPrevSelected-132]
+	_ = x[actPrint-133]
+	_ = x[actPut-134]
+	_ = x[actNextHistory-135]
+	_ = x[actNextSelected-136]
+	_ = x[actExecute-137]
+	_ = x[actExecuteSilent-138]
+	_ = x[actExecuteMulti-139]
+	_ = x[actSigStop-140]
+	_ = x[actFirst-141]
+	_ = x[actLast-142]
+	_ = x[actReload-143]
+	_ = x[actReloadSync-144]
+	_ = x[actDisableSearch-145]
+	_ = x[actEnableSearch-146]
+	_ = x[actSelect-147]
+	_ = x[actDeselect-148]
+	_ = x[actUnbind-149]
+	_ = x[actRebind-150]
+	_ = x[actToggleBind-151]
+	_ = x[actBecome-152]
+	_ = x[actShowHeader-153]
+	_ = x[actHideHeader-154]
+	_ = x[actBell-155]
+	_ = x[actExclude-156]
+	_ = x[actExcludeMulti-157]
+	_ = x[actAsync-158]
 }
 
-const _actionType_name = "actIgnoreactStartactClickactInvalidactBracketedPasteBeginactBracketedPasteEndactCharactMouseactBeginningOfLineactAbortactAcceptactAcceptNonEmptyactAcceptOrPrintQueryactBackwardCharactBackwardDeleteCharactBackwardDeleteCharEofactBackwardWordactCancelactChangeBorderLabelactChangeGhostactChangeHeaderactChangeFooteractChangeHeaderLabelactChangeFooterLabelactChangeInputLabelactChangeListLabelactChangeMultiactChangeNthactChangePointeractChangePreviewactChangePreviewLabelactChangePreviewWindowactChangePromptactChangeQueryactClearScreenactClearQueryactClearSelectionactCloseactDeleteCharactDeleteCharEofactEndOfLineactFatalactForwardCharactForwardWordactKillLineactKillWordactUnixLineDiscardactUnixWordRuboutactYankactBackwardKillWordactSelectAllactDeselectAllactToggleactToggleSearchactToggleAllactToggleDownactToggleUpactToggleInactToggleOutactToggleTrackactToggleTrackCurrentactToggleHeaderactToggleWrapactToggleMultiLineactToggleHscrollactTrackCurrentactToggleInputactHideInputactShowInputactUntrackCurrentactDownactUpactPageUpactPageDownactPositionactHalfPageUpactHalfPageDownactOffsetUpactOffsetDownactOffsetMiddleactJumpactJumpAcceptactPrintQueryactRefreshPreviewactReplaceQueryactToggleSortactShowPreviewactHidePreviewactTogglePreviewactTogglePreviewWrapactTransformactTransformBorderLabelactTransformGhostactTransformHeaderactTransformFooteractTransformHeaderLabelactTransformFooterLabelactTransformInputLabelactTransformListLabelactTransformNthactTransformPointeractTransformPreviewLabelactTransformPromptactTransformQueryactTransformSearchactBgTransformactBgTransformBorderLabelactBgTransformGhostactBgTransformHeaderactBgTransformFooteractBgTransformHeaderLabelactBgTransformFooterLabelactBgTransformInputLabelactBgTransformListLabelactBgTransformNthactBgTransformPointeractBgTransformPreviewLabelactBgTransformPromptactBgTransformQueryactBgTransformSearchactSearchactPreviewactPreviewTopactPreviewBottomactPreviewUpactPreviewDownactPreviewPageUpactPreviewPageDownactPreviewHalfPageUpactPreviewHalfPageDownactPrevHistoryactPrevSelectedactPrintactPutactNextHistoryactNextSelectedactExecuteactExecuteSilentactExecuteMultiactSigStopactFirstactLastactReloadactReloadSyncactDisableSearchactEnableSearchactSelectactDeselectactUnbindactRebindactToggleBindactBecomeactShowHeaderactHideHeaderactBellactExcludeactExcludeMultiactAsync"
+const _actionType_name = "actIgnoreactStartactClickactInvalidactBracketedPasteBeginactBracketedPasteEndactCharactMouseactBeginningOfLineactAbortactAcceptactAcceptNonEmptyactAcceptOrPrintQueryactBackwardCharactBackwardDeleteCharactBackwardDeleteCharEofactBackwardWordactCancelactChangeBorderLabelactChangeGhostactChangeHeaderactChangeFooteractChangeHeaderLabelactChangeFooterLabelactChangeInputLabelactChangeListLabelactChangeMultiactChangeNthactChangePointeractChangePreviewactChangePreviewLabelactChangePreviewWindowactChangePromptactChangeQueryactClearScreenactClearQueryactClearSelectionactCloseactDeleteCharactDeleteCharEofactEndOfLineactFatalactForwardCharactForwardWordactKillLineactKillWordactUnixLineDiscardactUnixWordRuboutactYankactBackwardKillWordactSelectAllactDeselectAllactToggleactToggleSearchactToggleAllactToggleDownactToggleUpactToggleInactToggleOutactToggleTrackactToggleTrackCurrentactToggleHeaderactToggleWrapactToggleMultiLineactToggleHscrollactTrackCurrentactToggleInputactHideInputactShowInputactUntrackCurrentactDownactUpactPageUpactPageDownactPositionactHalfPageUpactHalfPageDownactOffsetUpactOffsetDownactOffsetMiddleactJumpactJumpAcceptactPrintQueryactRefreshPreviewactReplaceQueryactToggleSortactShowPreviewactHidePreviewactTogglePreviewactTogglePreviewWrapactTransformactTransformBorderLabelactTransformGhostactTransformHeaderactTransformFooteractTransformHeaderLabelactTransformFooterLabelactTransformInputLabelactTransformListLabelactTransformNthactTransformPointeractTransformPreviewLabelactTransformPromptactTransformQueryactTransformSearchactBgTransformactBgTransformBorderLabelactBgTransformGhostactBgTransformHeaderactBgTransformFooteractBgTransformHeaderLabelactBgTransformFooterLabelactBgTransformInputLabelactBgTransformListLabelactBgTransformNthactBgTransformPointeractBgTransformPreviewLabelactBgTransformPromptactBgTransformQueryactBgTransformSearchactBgCancelactSearchactPreviewactPreviewTopactPreviewBottomactPreviewUpactPreviewDownactPreviewPageUpactPreviewPageDownactPreviewHalfPageUpactPreviewHalfPageDownactPrevHistoryactPrevSelectedactPrintactPutactNextHistoryactNextSelectedactExecuteactExecuteSilentactExecuteMultiactSigStopactFirstactLastactReloadactReloadSyncactDisableSearchactEnableSearchactSelectactDeselectactUnbindactRebindactToggleBindactBecomeactShowHeaderactHideHeaderactBellactExcludeactExcludeMultiactAsync"
 
-var _actionType_index = [...]uint16{0, 9, 17, 25, 35, 57, 77, 84, 92, 110, 118, 127, 144, 165, 180, 201, 225, 240, 249, 269, 283, 298, 313, 333, 353, 372, 390, 404, 416, 432, 448, 469, 491, 506, 520, 534, 547, 564, 572, 585, 601, 613, 621, 635, 649, 660, 671, 689, 706, 713, 732, 744, 758, 767, 782, 794, 807, 818, 829, 841, 855, 876, 891, 904, 922, 938, 953, 967, 979, 991, 1008, 1015, 1020, 1029, 1040, 1051, 1064, 1079, 1090, 1103, 1118, 1125, 1138, 1151, 1168, 1183, 1196, 1210, 1224, 1240, 1260, 1272, 1295, 1312, 1330, 1348, 1371, 1394, 1416, 1437, 1452, 1471, 1495, 1513, 1530, 1548, 1562, 1587, 1606, 1626, 1646, 1671, 1696, 1720, 1743, 1760, 1781, 1807, 1827, 1846, 1866, 1875, 1885, 1898, 1914, 1926, 1940, 1956, 1974, 1994, 2016, 2030, 2045, 2053, 2059, 2073, 2088, 2098, 2114, 2129, 2139, 2147, 2154, 2163, 2176, 2192, 2207, 2216, 2227, 2236, 2245, 2258, 2267, 2280, 2293, 2300, 2310, 2325, 2333}
+var _actionType_index = [...]uint16{0, 9, 17, 25, 35, 57, 77, 84, 92, 110, 118, 127, 144, 165, 180, 201, 225, 240, 249, 269, 283, 298, 313, 333, 353, 372, 390, 404, 416, 432, 448, 469, 491, 506, 520, 534, 547, 564, 572, 585, 601, 613, 621, 635, 649, 660, 671, 689, 706, 713, 732, 744, 758, 767, 782, 794, 807, 818, 829, 841, 855, 876, 891, 904, 922, 938, 953, 967, 979, 991, 1008, 1015, 1020, 1029, 1040, 1051, 1064, 1079, 1090, 1103, 1118, 1125, 1138, 1151, 1168, 1183, 1196, 1210, 1224, 1240, 1260, 1272, 1295, 1312, 1330, 1348, 1371, 1394, 1416, 1437, 1452, 1471, 1495, 1513, 1530, 1548, 1562, 1587, 1606, 1626, 1646, 1671, 1696, 1720, 1743, 1760, 1781, 1807, 1827, 1846, 1866, 1877, 1886, 1896, 1909, 1925, 1937, 1951, 1967, 1985, 2005, 2027, 2041, 2056, 2064, 2070, 2084, 2099, 2109, 2125, 2140, 2150, 2158, 2165, 2174, 2187, 2203, 2218, 2227, 2238, 2247, 2256, 2269, 2278, 2291, 2304, 2311, 2321, 2336, 2344}
 
 func (i actionType) String() string {
 	if i < 0 || i >= actionType(len(_actionType_index)-1) {