Fix iOS Simulator performance with Metal (#3156)

* Fix iOS Simulator performance with Metal

* Cross-platform build fix

* make DepthStencilModePrivate readonly

* rebase field from outer space

* Fix indentation and formatting in SKMetalView.cs

* Fix ObjCRuntime.Arch comparison in SKMetalView

---------

Co-authored-by: Matthew Leibowitz <[email protected]>

Author: taublast

source/SkiaSharp.Views/SkiaSharp.Views/Platform/Apple/SKMetalView.cs

@@ -32,6 +32,15 @@ event EventHandler IComponent.Disposed
 
 		private bool designMode;
 
+		private bool DepthStencilModePrivate =>
+		#if __MACCATALYST__
+			false;
+		#elif __MACOS__
+			true;
+		#else
+			ObjCRuntime.Runtime.Arch == ObjCRuntime.Arch.SIMULATOR;
+		#endif
+
 		private GRMtlBackendContext backendContext;
 		private GRContext context;
 
@@ -84,7 +93,16 @@ private void Initialize()
 
 			ColorPixelFormat = MTLPixelFormat.BGRA8Unorm;
 			DepthStencilPixelFormat = MTLPixelFormat.Depth32Float_Stencil8;
-			SampleCount = 1;
+			if (DepthStencilModePrivate)
+			{
+				DepthStencilStorageMode = MTLStorageMode.Private;
+				SampleCount = 4;
+			}
+			else
+			{
+				DepthStencilStorageMode = MTLStorageMode.Shared;
+				SampleCount = 2;
+			}
 			FramebufferOnly = false;
 			Device = device;
 			backendContext = new GRMtlBackendContext