add additional and default keywords to the TextMate grammar

[ginsbach]

This PR updates the TextMate grammar to contain the recently added additional and default keywords. This will improve syntax highlighting.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.