- Fix Metal validation error caused by CAMetalDrawable released before
MTLCommandBuffer is finished using it.
- When presenting, MVKPresentableSwapchainImage retains in-flight
CAMetalDrawable until MTLCommandBuffer completion.
- Fix memory leak of MVKFences and MVKSemaphores when a
swapchain image is acquired more than it is presented.
- Force MVKPresentableSwapchainImage to untrack any tracked fences or
semaphores when it is destroyed.
- Update MoltenVK version to 1.2.2.
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