Add a syntax tree view, for developing and debugging language support (#2601)

This PR adds a syntax tree view, which lets you view the syntax tree of
any layer in the active editor's `SyntaxMap`.

This view uses some new APIs that I added to Tree-sitter, which allow us
to efficiently render the syntax tree using a `UniformList`. Tree-sitter
PR: https://github.com/tree-sitter/tree-sitter/pull/2316

![Screen Shot 2023-06-12 at 3 33 36
PM](https://github.com/zed-industries/zed/assets/326587/2a27ee7b-bf29-4b3b-bfa8-fb47f97a2785)

Release Notes:

- Added a *syntax tree view* that shows Zed's internal syntax tree(s)
for the active editor. You can open it running the `debug: open syntax
tree view` command from the command palette.