vim-patch:9.1.1764: filetype: CODEOWNERS file not recognized (#35789)

Problem:  filetype: CODEOWNERS file not recognized
Solution: Detect CODEOWNERS file as codeowners filetype, include a
          syntax and filetype plugin (Jon Parise).

CODEOWNERS files define code ownership rules for GitHub-hosted (and
other) repositories. The syntax is similar to 'gitignore' files but
differs in enough ways to warrant its own filetype.

References:
- https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners

closes: vim/vim#18299

817e4d3ee6

Co-authored-by: Jon Parise <jon@indelible.org>

runtime/syntax/codeowners.vim

@@ -0,0 +1,23 @@
+" Vim syntax file
+" Language:	codeowners
+" Maintainer:	Jon Parise <jon@indelible.org>
+" Last Change:	2025 Sep 14
+
+if exists('b:current_syntax')
+  finish
+endif
+
+" Comments
+syn match codeownersComment /#.*$/ contains=codeownersTodo,@Spell
+syn keyword codeownersTodo TODO FIXME XXX contained
+
+" Patterns
+syn match codeownersPattern /^#\@![^#]*/ contains=codeownersGlob
+syn match codeownersGlob /^\S\+/ contained nextgroup=codeownersOwner skipwhite
+syn match codeownersOwner /\S\+/ contained nextgroup=codeownersOwner skipwhite
+
+hi def link codeownersComment Comment
+hi def link codeownersOwner Identifier
+hi def link codeownersTodo Todo
+
+let b:current_syntax = 'codeowners'