feat(queries/highlight): highlight built-in functions as @function.builtin

[jimeh]

This PR supersedes #61 by fixing the scoping issue it has. I have been using this query since March 10th in my own Emacs config without any issues.

Checklist:

• All tests pass in CI.
• There are sufficient tests for the new fix/feature.
• Grammar rules have not been renamed unless absolutely necessary.
• The conflicts section hasn't grown too much.
• The parser size hasn't grown too much (check the value of STATE_COUNT in src/parser.c).

[aryx]

@maxbrunsfeld any idea why we don't get any more CI jobs to check the PRs are correct?