The [MTLDevice sampleTimestamps:gpuTimestamp:] function turns out to be
synchronized with other queue activities, and can block GPU execution
if it is called between MTLCommandBuffer submissions. On non-Apple-Silicon
devices, it was called before and after every vkQueueSubmit() submission,
to track the correlation between GPU and CPU timestamps, and was delaying
the start of GPU work on the next submission (on Apple Silicon, both
CPU & GPU timestamps are specified in nanoseconds, and the call was bypassed).
Move timestamp correlation from vkQueueSubmit() to
vkGetPhysicalDeviceProperties(), where it is used to update
VkPhysicalDeviceLimits::timestampPeriod on non-Apple-Silicon devices.
Delegate MVKPhysicalDevice::getProperties(VkPhysicalDeviceProperties2*)
to MVKPhysicalDevice::getProperties(VkPhysicalDeviceProperties*), plus
minimize wasted effort if pNext is empty (unrelated).
Move the declaration of several MVKPhysicalDevice member structs to
potentially reduce member spacing (unrelated).
dd31587337