This PR changes the default LSP for
[someone13574/zed-verilog-extension](https://github.com/someone13574/zed-verilog-extension)
to [slang-server](https://github.com/hudson-trading/slang-server), which
was added a while ago but disabled due to being relatively new and
having a few issues. Since those issues have been resolved, it is now
becoming the default, replacing `verible` and `veridian`, which were
previously used together.

Additionally this is being done to disable `svls` by default, as it was
added in https://github.com/zed-industries/extensions/pull/6820.

Release Notes:

- N/A

---------

Co-authored-by: Kirill Bulatov <kirill@zed.dev>