Only set `MTLTextureUsagePixelFormatView` if this bit is set. This
should reduce the usage of this bit, which disables lossless compression
on Apple GPUs, in many cases.
We continue to set it anyway for `VK_IMAGE_USAGE_TRANSFER_SRC_BIT`; this
is because we create those texture views on the application's behalf, to
implement `vkCopyImage()` where the source and destination formats do
not agree. We also continue to set it for depth/stencil formats; Metal
requires it in order to use only the stencil aspect in a view.
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