feat(search): Add Syntax Highlighting for Hack Language

[mmanela]

As part of GRAPH-205 for support Hack language, this PR adds Syntax highlighting.
Fixes GRAPH-617

Key notes

1. Added a reference to the Hack tree-sitter package
2. Add a highlights query for identifying the items to highlight (Note: I built our version off of the solid foundation found in the Neovim tree sitter repo. But iterated a decent amount for how we would like it highlighted.
3. Added updated test cases trying to cover many interesting languages features. Hack is a large language and I am not covering everything possible but many key features.
4. It seems there are some gaps in the upstream tree-sitter grammar such as doesn't support module statement and doesn't support string interpolation (parses just as string)

Upstream bugs filed

• [BUG] nameof operator missing from the gammar slackhq/tree-sitter-hack#68
• [BUG] String Interpolation is not supported slackhq/tree-sitter-hack#69
• [BUG] Module membership declarations are not supported in the grammar slackhq/tree-sitter-hack#70
• Using nameof syntax leads to parse errors facebook/hhvm#9447

Screenshots

Test plan

• Unit tests
• Validate UI and ensure it looks appropriate

[varungandhi-src]

It seems there are some gaps in the upstream tree-sitter grammar such as doesn't support module statement and doesn't support string interpolation (parses just as string)

Please file 1-2 issues upstream so that we can link them here.

[muglug]

Thanks for doing this!

I know you have the tree-sitter grammar already, but we also have a slightly-more-up-to-date TextMate grammar here that supports module and more: https://github.com/slackhq/vscode-hack/blob/master/syntaxes/hack.json

[mmanela]

@muglug Thanks. Our highlighting is based on tree-sitter, so would be great to get the missing parts added to the hack tree-sitter lib. I plan to file issues there on what I found

[muglug]

Sounds good — at Slack we’re not yet using modules, so that’s no sort of blocker. Once we start considering that we’ll push necessary changes to the tree-sitter grammar.

[mmanela]

Yea I think the bigger annoyance will be the lack of string interpolation support

[varungandhi-src]

Please go through https://docs.hhvm.com and identify the different syntax forms which aren't being tested and add tests for those. I've identified some which are missing, I haven't tried to be exhaustive.