This PR adjusts the heading levels in the docs, as some of them weren't
following the right hierarchy.
I also formatted all of the docs with Prettier.
Release Notes:
- N/A
This pull request implements the following documentation changes:
- [x] Copy existing language settings docs from old docs repo
- [x] Add new pages for Zig, Haskell, Gleam, Deno and PureScript
- [x] Add `rust-analyzer` target directory section to Rust language page
Release Notes:
- Added initial language settings documentation
([#4264](https://github.com/zed-industries/zed/issues/4264)).
