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/copilot/src/copilot.rs

@@ -383,8 +383,16 @@ impl Copilot {
         use lsp::FakeLanguageServer;
         use node_runtime::FakeNodeRuntime;
 
-        let (server, fake_server) =
-            FakeLanguageServer::new("copilot".into(), Default::default(), cx.to_async());
+        let (server, fake_server) = FakeLanguageServer::new(
+            LanguageServerBinary {
+                path: "path/to/copilot".into(),
+                arguments: vec![],
+                env: None,
+            },
+            "copilot".into(),
+            Default::default(),
+            cx.to_async(),
+        );
         let http = util::http::FakeHttpClient::create(|_| async { unreachable!() });
         let node_runtime = FakeNodeRuntime::new();
         let this = cx.new_model(|cx| Self {