`zls` should be used as the `zig` fixer, not `zig fmt`

Re: https://github.com/dense-analysis/ale/issues/2484

Since it's using LSP rather than a straight binary, it's probably a good idea to keep both.

I have a Hello World vim-ale + LSP example that can be referenced for a PR for this:
https://github.com/BeyondCodeBootcamp/vim-ale-hello-world

Specifically:

- `~/.vim/pack/plugins/start/ale/autoload/ale/fix/registry.vim`:
https://github.com/BeyondCodeBootcamp/vim-ale-hello-world/blob/60b46555c3e812f1fe5c1ace00a7b96003714445/plugin/hello_world.vim#L9-L14

- `~/.vim/pack/plugins/start/ale/ale_linters/zig/zls.vim`:
https://github.com/BeyondCodeBootcamp/vim-ale-hello-world/blob/60b46555c3e812f1fe5c1ace00a7b96003714445/ale_linters/hellolang/hello_lint.vim#L21-L32

- `~/.vim/pack/plugins/start/ale/autoload/ale/fixers/zls.vim`:
https://github.com/BeyondCodeBootcamp/vim-ale-hello-world/blob/60b46555c3e812f1fe5c1ace00a7b96003714445/autoload/hello_world/fixers/hello_fmt.vim#L8-L14