## Summary

This PR enables extension authors to disable language servers from the
`extension.toml` as opposed to requiring a change to Zed's default
settings.

With this in, we no longer need to ship default enabled servers for a
given language and can instead resort to extension authors disabling
those in their extension. This gives extension authors more control and
also finally removes the need to link Zed version releases to extension
releases in cases where the extension wants to add a new language
server.

## Testing

Aside from the added tests, also ran a local build and tested this
against the kotlin extension. Worked as I would expect it to.

## Self-review

- [X] I've reviewed my diff for quality, security, reliability, and
performance.
- [-] UI changes follow the
[checklist](https://zed.dev/docs/development/ui-checklist).
- [X] Tests cover the new or changed behavior.

Release Notes:

- Added the possibility for language server extensions to configure
which language servers are enabled/disabled by default. Visit
https://zed.dev/docs/extensions/languages.md#opt-in-language-servers for
more information.

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Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>
Co-authored-by: zed-zippy[bot] <234243425+zed-zippy[bot]@users.noreply.github.com>