Add shared test cases with vim-svelte-plugin

Name cases for scenarios also in vim-svelte-plugin as shared-*, adding
one for multiline tags. test/shared.sh lists shared cases in only one
of the plugins, as a warning in a separate job on GitHub Actions.

test/shared.sh

@@ -0,0 +1,30 @@
+#!/bin/sh
+# List shared-* test cases missing in either vim-svelte-plugin or
+# vim-vue-plugin. Both plugins work in the same way for blocks, so a case for
+# a scenario in one plugin should be in the other with the same name. Only
+# warn, as the other plugin may be updated later
+#   ./test/shared.sh
+cd "$(dirname "$0")/.." || exit 1
+other=vim-svelte-plugin
+
+dir=test/other/$other
+rm -rf "$dir"
+git clone -q --depth 1 "https://github.com/leafOfTree/$other" "$dir" || exit 0
+
+list() {
+  ls "$1"/test/cases/shared-*.vim 2>/dev/null | sed 's#.*/##; s#\.vim$##' | sort
+}
+list . > test/other/mine
+list "$dir" > test/other/theirs
+
+missing=0
+for name in $(comm -23 test/other/mine test/other/theirs); do
+  echo "::warning::$name is not in $other"
+  missing=1
+done
+for name in $(comm -13 test/other/mine test/other/theirs); do
+  echo "::warning::$name in $other is not here"
+  missing=1
+done
+[ $missing -eq 0 ] && echo "Shared cases are the same as $other"
+exit 0