Make block_with_timeout more robust (#11670)

The previous implementation relied on a background thread to wake up the
main thread,
which was prone to priority inversion under heavy load.

In a synthetic test, where we spawn 200 git processes while doing a 5ms
timeout, the old version blocked for 5-80ms, the new version blocks for
5.1-5.4ms.

Release Notes:

- Improved responsiveness of the main thread under high system load

crates/gpui/src/platform.rs

@@ -240,8 +240,7 @@ pub trait PlatformDispatcher: Send + Sync {
     fn dispatch(&self, runnable: Runnable, label: Option<TaskLabel>);
     fn dispatch_on_main_thread(&self, runnable: Runnable);
     fn dispatch_after(&self, duration: Duration, runnable: Runnable);
-    fn tick(&self, background_only: bool) -> bool;
-    fn park(&self);
+    fn park(&self, timeout: Option<Duration>) -> bool;
     fn unparker(&self) -> Unparker;
 
     #[cfg(any(test, feature = "test-support"))]