For a combined depth-stencil format in a MVKImageView attachment with
VK_IMAGE_ASPECT_STENCIL_BIT, the attachment format may have been swizzled
to a stencil-only format. In this case, we want to guard against an attempt
to store the non-existent depth component.
Pass MVKImageView attachment to MVKRenderPassAttachment::encodeStoreAction()
and MVKRenderPassAttachment::populateMTLRenderPassAttachmentDescriptor() to
check attachment depth format component.
Consolidate calls to MVKImageView::populateMTLRenderPassAttachmentDescriptor() by calling
it from within MVKRenderPassAttachment::populateMTLRenderPassAttachmentDescriptor().
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