fix(filetype): normalize full path before matching #32227

Problem:
On Windows, treesitter query files are not recognized as such when
opened from inside their directory, because the full path returned from
fnamemodify(_, ':p') contains backslashes, while the filetype patterns
expect forward slashes.

Solution:
Normalize the result of fnamemodify(_, ':p') before trying to match it
to filetype patterns.

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

runtime/lua/vim/filetype.lua

@@ -2565,6 +2565,15 @@ local function normalize_path(path, as_pattern)
   return normal
 end
 
+local abspath = function(x)
+  return fn.fnamemodify(x, ':p')
+end
+if fn.has('win32') == 1 then
+  abspath = function(x)
+    return (fn.fnamemodify(x, ':p'):gsub('\\', '/'))
+  end
+end
+
 --- @class vim.filetype.add.filetypes
 --- @inlinedoc
 --- @field pattern? vim.filetype.mapping
@@ -2873,7 +2882,7 @@ function M.match(args)
     name = normalize_path(name)
 
     -- First check for the simple case where the full path exists as a key
-    local path = fn.fnamemodify(name, ':p')
+    local path = abspath(name)
     ft, on_detect = dispatch(filename[path], path, bufnr)
     if ft then
       return ft, on_detect