Reduce GPU memory usage (#7319)

This pull request decreases the size of each instance buffer and shares
instance buffers across windows.

Release Notes:

- Improved GPU memory usage.

---------

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

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

@@ -459,6 +459,7 @@ impl MacWindow {
         handle: AnyWindowHandle,
         options: WindowOptions,
         executor: ForegroundExecutor,
+        instance_buffer_pool: Arc<Mutex<Vec<metal::Buffer>>>,
     ) -> Self {
         unsafe {
             let pool = NSAutoreleasePool::new(nil);
@@ -535,7 +536,7 @@ impl MacWindow {
                 native_window,
                 native_view: NonNull::new_unchecked(native_view as *mut _),
                 display_link,
-                renderer: MetalRenderer::new(true),
+                renderer: MetalRenderer::new(instance_buffer_pool),
                 kind: options.kind,
                 request_frame_callback: None,
                 event_callback: None,