zink: make physical device functions use a dynamic function pointers.

zink: make physical device functions use a dynamic function pointers.

vkGetPhysicalDeviceFeatures2 and vkGetPhysicalDeviceProperties2 are not present on some MoltenVK versions.
VK_KHR_get_physical_device_properties2 exposes the KHR versions of the same functions.
These cannot be used via static linking, so we have to dynamically detect the loader version and then the extension
to work out which pointers to use.

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7447>