Fix iOS Simulator performance with Metal

[taublast]

Had iOS simulator lagging on M1 at 9 fps with SKGLView, so had to adjust its platform-related code for iOS to unlock 60 fps.
Just followed Apple guidelines for simulator: https://developer.apple.com/documentation/metal/developing-metal-apps-that-run-in-simulator?language=objc

replacing SampleCount = 1; (no MSAA) inside SKMetalView with:

			if (DeviceInfo.Current.DeviceType == DeviceType.Virtual)
			{
				DepthStencilStorageMode = MTLStorageMode.Private;
				SampleCount = 4;
			}
			else
			{
				DepthStencilStorageMode = MTLStorageMode.Shared;
				SampleCount = 2;
			}

Works fine in DrawnUi now, wanted to share.

[dotnet-policy-service]

Hey there @taublast! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[mattleibow]

/azp run

[azure-pipelines]

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