The same set of CTS tests either fails or passes on different GPUs
based on whether or not we adjust float clear colors by one ULP.
Add MVKFloatRounding enum.
Add MVKPhysicalDeviceMetalFeatures::clearColorFloatRounding.
Disable ULP adjustment for clear colors on Apple Silicon.
For consistency and to simplify bookkeepping, calculate
clear color ULP adjustment from bit width of format component.
Update MoltenVK version to 1.1.5.
Update VK_MVK_MOLTENVK_SPEC_VERSION to 32.
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