Start to split out initialization and registration (#21787)

Still TODO:

* [x] Factor out `start_language_server` so we can call it on register
(instead of on detect language)
* [x] Only call register in singleton editors (or when
editing/go-to-definition etc. in a multibuffer?)
* [x] Refcount on register so we can unregister when no buffer remain
* [ ] (maybe) Stop language servers that are no longer needed after some
time

Release Notes:

- Fixed language servers starting when doing project search
- Fixed high CPU usage when ignoring warnings in the diagnostics view

---------

Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>
Co-authored-by: Cole <cole@zed.dev>

crates/proto/src/proto.rs

@@ -373,6 +373,7 @@ messages!(
     (SyncExtensions, Background),
     (SyncExtensionsResponse, Background),
     (InstallExtension, Background),
+    (RegisterBufferWithLanguageServers, Background),
 );
 
 request_messages!(
@@ -499,6 +500,7 @@ request_messages!(
     (CancelLanguageServerWork, Ack),
     (SyncExtensions, SyncExtensionsResponse),
     (InstallExtension, Ack),
+    (RegisterBufferWithLanguageServers, Ack),
 );
 
 entity_messages!(
@@ -584,6 +586,7 @@ entity_messages!(
     ActiveToolchain,
     GetPathMetadata,
     CancelLanguageServerWork,
+    RegisterBufferWithLanguageServers,
 );
 
 entity_messages!(