Allow canceling in-progress language server work (e.g. cargo check) (#13173)

Release Notes:

- Added a more detailed message in place of the generic `checking...`
messages when Rust-analyzer is running.
- Added a rate limit for language server status messages, to reduce
noisiness of those updates.
- Added a `cancel language server work` action which will cancel
long-running language server tasks.

---------

Co-authored-by: Richard <richard@zed.dev>

script/zed-local

@@ -172,7 +172,7 @@ setTimeout(() => {
       env: Object.assign({}, process.env, {
         ZED_IMPERSONATE: users[i],
         ZED_WINDOW_POSITION: position,
-        ZED_STATELESS: isStateful && i == 0 ? "1" : "",
+        ZED_STATELESS: isStateful && i == 0 ? "" : "1",
         ZED_ALWAYS_ACTIVE: "1",
         ZED_SERVER_URL: "http://localhost:3000",
         ZED_RPC_URL: "http://localhost:8080/rpc",