[FEATURE] Highlighting Queries Improvements

[Kilenaitor]

Description

Hi! I read/write a lot of Hack code in my day-to-day. My primary editor is Neovim and I've been hoping to leverage tree-sitter to power syntax highlighting. However, the highlighting queries for Hack are pretty bare-bones: https://github.com/slackhq/tree-sitter-hack/blob/main/queries/highlights.scm

I was curious if you all would accept contributions to at the very least the highlight queries to be more in line with other tree-sitter grammars (here's PHP for comparison).

I'd be potentially interested in augmenting the grammar or the parser as well to allow for more fine-tuned highlight queries, but I'd of course defer to you all for anything backwards incompatible.

Thank you!

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

[4e554c4c]

treesitter highlighting for Hack in neovim works pretty great. It uses a different highlight query than this project provides: https://github.com/nvim-treesitter/nvim-treesitter/blob/master/queries/hack/highlights.scm
we really just need to sync that file with the highlights provided in this repository.
Another good thing to add would be a locals.scm, since Hack has odd scoping rules.

IMO this is the last thing stopping tree-sitter-hack from being a "maintained" language for nvim-treesitter, it's just been on my backlog for a long time.