Add initial support for defining language server adapters in WebAssembly-based extensions (#8645)

This PR adds **internal** ability to run arbitrary language servers via
WebAssembly extensions. The functionality isn't exposed yet - we're just
landing this in this early state because there have been a lot of
changes to the `LspAdapter` trait, and other language server logic.

## Next steps

* Currently, wasm extensions can only define how to *install* and run a
language server, they can't yet implement the other LSP adapter methods,
such as formatting completion labels and workspace symbols.
* We don't have an automatic way to install or develop these types of
extensions
* We don't have a way to package these types of extensions in our
extensions repo, to make them available via our extensions API.
* The Rust extension API crate, `zed-extension-api` has not yet been
published to crates.io, because we still consider the API a work in
progress.

Release Notes:

- N/A

---------

Co-authored-by: Marshall <marshall@zed.dev>
Co-authored-by: Nathan <nathan@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/collab/src/tests/random_project_collaboration_tests.rs

@@ -1021,7 +1021,7 @@ impl RandomizedTest for ProjectCollaborationTest {
     }
 
     async fn on_client_added(client: &Rc<TestClient>, _: &mut TestAppContext) {
-        let mut language = Language::new(
+        client.language_registry().add(Arc::new(Language::new(
             LanguageConfig {
                 name: "Rust".into(),
                 matcher: LanguageMatcher {
@@ -1031,9 +1031,10 @@ impl RandomizedTest for ProjectCollaborationTest {
                 ..Default::default()
             },
             None,
-        );
-        language
-            .set_fake_lsp_adapter(Arc::new(FakeLspAdapter {
+        )));
+        client.language_registry().register_fake_lsp_adapter(
+            "Rust",
+            FakeLspAdapter {
                 name: "the-fake-language-server",
                 capabilities: lsp::LanguageServer::full_capabilities(),
                 initializer: Some(Box::new({
@@ -1132,9 +1133,8 @@ impl RandomizedTest for ProjectCollaborationTest {
                     }
                 })),
                 ..Default::default()
-            }))
-            .await;
-        client.app_state.languages.add(Arc::new(language));
+            },
+        );
     }
 
     async fn on_quiesce(_: &mut TestServer, clients: &mut [(Rc<TestClient>, TestAppContext)]) {