Add Zig support (#6690)

This PR adds support for Zig with the official LSP (ZLS) and the
treesitter grammar listed on the
[website](https://tree-sitter.github.io/tree-sitter/). I've tested this
on a few large codebases and go to definition, completion, and hover
overlays all seem to work fine with no error logs.

![Screenshot 2024-01-24 at 20 17
18](https://github.com/zed-industries/zed/assets/11731580/be7b4f1d-878e-4e3e-839b-a5f962df7555)

The highlights are adapted from the tree sitter repository which target
neovim I think, I've fixed a handful of issues and the highlighting is
looking pretty good but need to do more testing.

Release Notes:
- Added Zig support with zls
[#5300](https://github.com/zed-industries/zed/issues/5300).