Fix syntax highlighting of git commit messages (#26988)

- Load syntax colors into commit message editors
- Fix name mismatches that were preventing the git commit grammar and
language config from being matched up

Release Notes:

- Fixed git commit messages not being syntax-highlighted

crates/languages/src/gitcommit/config.toml

@@ -1,5 +1,5 @@
 name = "Git Commit"
-grammar = "git_commit"
+grammar = "gitcommit"
 path_suffixes = [
   "TAG_EDITMSG",
   "MERGE_MSG",