runtime(vim): Improve Vim9 and legacy-script comment highlighting (#13104)

This is a first-pass attempt to limit matching of Vim9 and legacy-script
comments to the appropriate syntactic contexts.

Vim9-script comments are highlighted at top level in a Vim9-script file,
in all :def functions, and in all :autocmd and :commmand command blocks.
Legacy-script comments are highlighted at top level in a legacy script
file, in all :func functions and in the Vim9-script preamble before the
:vim9script marker command.

Fixes #13047, #11307 and #9587.

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index f8ea87e..ac127f0 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -222,6 +222,7 @@
 runtime/ftplugin/typescriptreact.vim	@dkearns
 runtime/ftplugin/unison.vim		@chuwy
 runtime/ftplugin/vdf.vim		@ObserverOfTime
+runtime/ftplugin/vim.vim		@dkearns
 runtime/ftplugin/wast.vim		@rhysd
 runtime/ftplugin/wget.vim		@dkearns
 runtime/ftplugin/wget2.vim		@dkearns