add: ⟨...⟩ as possible brackets

[Quoteme]

Hi dear treesitter/typst community,

inner products are commonly denoted using $angle.l ..., ... angle.r$ or as of recently $chevron.l ..., ... chevron.r$ in typst documents.
Another valid method it seems is to use unicode characters like $⟨..., ...⟩$ instead (imo more readable).

Especially in deeply nested equations using a plugin like HiPhish/rainbow-delimiters.nvim is a good way to not get lost. It does however depend on the underlying treesitter parser being able to identify ⟨ and ⟩ as bracket pairs, just like ( and ). Currently, this was not the case.

I made some changes so that ⟨ and ⟩ does get recognised as a bracket pair, resulting in this pull request. Could you please skim over it and possibly merge it? I am completely new to treesitter parsers, so I am not sure if my code is well written, but nonetheless I tested it and it works:

Before:

After:

PS: I accidentally started development from the master branch. I will fix this when I get to it, hopefully asap.