Add syntax highlighting queries

[Wilfred]

Summary

Add basic syntax highlighting for comments, strings, common keywords and types.

Requirements (place an x in each [ ])

• [x] I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• [x] I've read and agree to the Code of Conduct.

[CLAassistant]

All committers have signed the CLA.

[brownierin]

Thanks for contributing! My apologies for the delay; a good chunk of this grammar was written during internships last summer, and we're getting back into the swing of it now.

We haven't done much with syntax highlighting in this tree-sitter grammar as we're using it to parse hack code for use with Semgrep. Based on the docs, this looks good to me. I also ran tree-sitter highlight on some of our test hack files; it's outputting correctly. :+1:

[frankeld]

Thanks for this contribution! I will add that as we expand syntax highlighting, we might want to consider adding tests, along with organizing our .scm files with headers (ex. ; Keywords) consistent with the other tree-sitter packages.

We will also want to update language configuration (especially language detection) to support hack files as described here: https://tree-sitter.github.io/tree-sitter/syntax-highlighting#language-configuration