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/zed/src/main.rs

@@ -178,6 +178,7 @@ fn main() {
         extension::init(
             fs.clone(),
             http.clone(),
+            node_runtime.clone(),
             languages.clone(),
             ThemeRegistry::global(cx),
             cx,

crates/zed/src/zed.rs

@@ -1594,7 +1594,7 @@ mod tests {
         app_state
             .fs
             .as_fake()
-            .insert_file("/root/a.txt", "changed".to_string())
+            .insert_file("/root/a.txt", b"changed".to_vec())
             .await;
 
         cx.run_until_parked();