Restore bracketed paste mode instead of forcing it off

Ask the terminal whether the mode is already on (DECRQM) and put it back
that way on exit. Forcing it off broke pasting in shells that run fzf
from a line editor widget, which enable the mode only when the editor
starts. Terminals that do not answer fall back to disabling it.

- Startup queries go out in one write, cursor position last. Every
  terminal answers DSR, so its reply bounds the wait: a paste reply
  still missing by then means the terminal does not know the query.
- Bound the first read with select(2). Terminals that never answer
  escape sequences, such as FreeBSD virtual terminals, blocked startup
  until a key was pressed, and that keystroke was then discarded.

Fix #4887
Fix #2860
Fix #976

src/tui/light_windows.go

@@ -151,6 +151,13 @@ func (r *LightRenderer) findOffset() (row int, col int) {
 	return int(bufferInfo.CursorPosition.Y), int(bufferInfo.CursorPosition.X)
 }
 
+// The console API answers for the cursor, and there is no reply to parse for
+// bracketed paste, so fzf keeps disabling the mode on exit here.
+func (r *LightRenderer) queryStartup() (row int, col int, pasteWasSet *bool) {
+	row, col = r.findOffset()
+	return
+}
+
 func (r *LightRenderer) getch(cancellable bool, nonblock bool) (int, getCharResult) {
 	if !nonblock && !cancellable {
 		bc := <-r.ttyinChannel