Maintain smooth frame rates when ProMotion and direct mode are enabled (#7305)

This is achieved by starting a `CADisplayLink` that will invoke the
`on_request_frame` callback at the refresh interval of the display.

We only actually draw frames when the window was dirty, or for 2 extra
seconds after the last input event to ensure ProMotion doesn't downclock
the refresh rate when the user is actively interacting with the window.

Release Notes:

- Improved performance when using a ProMotion display with fast key
repeat rates.

---------

Co-authored-by: Nathan Sobo <nathan@zed.dev>

crates/gpui/src/platform/test/window.rs

@@ -282,8 +282,6 @@ impl PlatformWindow for TestWindow {
         unimplemented!()
     }
 
-    fn invalidate(&self) {}
-
     fn draw(&self, _scene: &crate::Scene) {}
 
     fn sprite_atlas(&self) -> sync::Arc<dyn crate::PlatformAtlas> {