fix(runtime): let matchit and matchparen skips fallback on treesitter captures

When treesitter is enabled, by default syntax groups are not defined, but these
groups are used to identify where to skip matches in matchit and matchparen.

This patch does three things:
1. If syntax is enabled regardless of treesitter (`vim.bo.syntax='on'`):
   Use original implementation.
2. If treesitter is enabled and syntax is not:
   Match the syntax groups (i.e. `comment\|string`) against treesitter captures
   to check for skipped groups.
3. Add an explicit treesitter syntax for marking captures to skip:
   matchit uses `b:match_skip` to determine what counts as skippable
   Where 's:comment\|string' uses a match of the named syntax groups against
   a regex match of comment\|string, 't:comment\|string' now uses vim regex
   to match against the names of the treesitter capture groups.

runtime/pack/dist/opt/matchit/autoload/matchit.vim

@@ -222,6 +222,7 @@ function matchit#Match_wrapper(word, forward, mode) range
   let view = winsaveview()
   call cursor(0, curcol + 1)
   if skip =~ 'synID' && !(has("syntax") && exists("g:syntax_on"))
+        \ || skip =~ 'v:lua.vim.treesitter' && !exists('b:ts_highlight')
     let skip = "0"
   else
     execute "if " .. skip .. "| let skip = '0' | endif"
@@ -678,6 +679,7 @@ fun! matchit#MultiMatch(spflag, mode)
   let middlepat = substitute(middlepat, ',', '\\|', 'g')
 
   if skip =~ 'synID' && !(has("syntax") && exists("g:syntax_on"))
+        \ || skip =~ 'v:lua.vim.treesitter' && !exists('b:ts_highlight')
     let skip = '0'
   else
     try
@@ -760,10 +762,16 @@ endfun
 "   S:foo becomes (current syntax item) !~ foo
 "   r:foo becomes (line before cursor) =~ foo
 "   R:foo becomes (line before cursor) !~ foo
+"   t:foo becomes (current treesitter captures) =~ foo
+"   T:foo becomes (current treesitter captures) !~ foo
 fun! s:ParseSkip(str)
   let skip = a:str
   if skip[1] == ":"
-    if skip[0] ==# "s"
+    if skip[0] ==# "t" || skip[0] ==# "s" && &syntax != 'on' && exists("b:ts_highlight")
+      let skip = "match(v:lua.vim.treesitter.get_captures_at_cursor(), '" .. strpart(skip,2) .. "') != -1"
+    elseif skip[0] ==# "T" || skip[0] ==# "S" && &syntax != 'on' && exists("b:ts_highlight")
+      let skip = "match(v:lua.vim.treesitter.get_captures_at_cursor(), '" .. strpart(skip,2) .. "') == -1"
+    elseif skip[0] ==# "s"
       let skip = "synIDattr(synID(line('.'),col('.'),1),'name') =~? '" ..
         \ strpart(skip,2) .. "'"
     elseif skip[0] ==# "S"

runtime/pack/dist/opt/matchit/doc/matchit.txt

@@ -237,6 +237,8 @@ supported by matchit.vim:
 	S:foo becomes (current syntax item) !~ foo
 	r:foo becomes (line before cursor) =~ foo
 	R:foo becomes (line before cursor) !~ foo
+	t:foo becomes (current treesitter captures) =~ foo
+	T:foo becomes (current treesitter captures) !~ foo
 (The "s" is meant to suggest "syntax", and the "r" is meant to suggest
 "regular expression".)
 

runtime/plugin/matchparen.vim

@@ -109,6 +109,10 @@ func s:Highlight_Matching_Pair()
 
   if !has("syntax") || !exists("g:syntax_on")
     let s_skip = "0"
+  elseif exists("b:ts_highlight") && &syntax != 'on'
+    let s_skip = "match(v:lua.vim.treesitter.get_captures_at_cursor(), '"
+          \ .. 'string\|character\|singlequote\|escape\|symbol\|comment'
+          \ .. "') != -1"
   else
     " Build an expression that detects whether the current cursor position is
     " in certain syntax types (string, comment, etc.), for use as