gpui: Enable direct-to-display optimization for metal (#45434)

Continuing of #44334 

I removed disabling of vsync which was causing jitter on some external
displays

cc: @maxbrunsfeld @Anthony-Eid 

Release Notes:

- Mark metal layers opaque for non-transparent windows to allow
direct-to-display when supported

Signed-off-by: Marco Mihai Condrache <52580954+marcocondrache@users.noreply.github.com>

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

@@ -46,9 +46,9 @@ pub unsafe fn new_renderer(
     _native_window: *mut c_void,
     _native_view: *mut c_void,
     _bounds: crate::Size<f32>,
-    _transparent: bool,
+    transparent: bool,
 ) -> Renderer {
-    MetalRenderer::new(context)
+    MetalRenderer::new(context, transparent)
 }
 
 pub(crate) struct InstanceBufferPool {
@@ -128,7 +128,7 @@ pub struct PathRasterizationVertex {
 }
 
 impl MetalRenderer {
-    pub fn new(instance_buffer_pool: Arc<Mutex<InstanceBufferPool>>) -> Self {
+    pub fn new(instance_buffer_pool: Arc<Mutex<InstanceBufferPool>>, transparent: bool) -> Self {
         // Prefer low‐power integrated GPUs on Intel Mac. On Apple
         // Silicon, there is only ever one GPU, so this is equivalent to
         // `metal::Device::system_default()`.
@@ -152,7 +152,9 @@ impl MetalRenderer {
         let layer = metal::MetalLayer::new();
         layer.set_device(&device);
         layer.set_pixel_format(MTLPixelFormat::BGRA8Unorm);
-        layer.set_opaque(false);
+        // Support direct-to-display rendering if the window is not transparent
+        // https://developer.apple.com/documentation/metal/managing-your-game-window-for-metal-in-macos
+        layer.set_opaque(!transparent);
         layer.set_maximum_drawable_count(3);
         unsafe {
             let _: () = msg_send![&*layer, setAllowsNextDrawableTimeout: NO];
@@ -352,8 +354,8 @@ impl MetalRenderer {
         }
     }
 
-    pub fn update_transparency(&self, _transparent: bool) {
-        // todo(mac)?
+    pub fn update_transparency(&self, transparent: bool) {
+        self.layer.set_opaque(!transparent);
     }
 
     pub fn destroy(&self) {