(macOS arm64) Support loading VK ICDs (in preparation for KosmicKrisp), fix arm64 CI fails

[schm1dtmac]

This PR makes some key changes to the arm64 macOS buildscripts, alongside changes to Vulkan init code on Mac, to enable linking these builds to the Vulkan Loader instead of MoltenVK directly, and then loading any installable-client-driver (ICD) (including so-called 'portability' ICDs like MoltenVK).
Notes:
I've switched swapchains to use VK_EXT_metal_surface for future compatibility with KosmicKrisp, but as this ext requires a CAMetalLayer I've had to add a little OBJC shim to get the metal layer out of the NSView. Unaware of any better alternatives atm.
For instance init I've had to force the 'fast' path on macOS to load 2 extensions needed so that 'portability'/non-conformant drivers like MoltenVK get detected on startup.
I haven't changed anything about the Intel build scripts given they will only have one driver option for the remainder of Intel macOS' life (MVK, as KK only supports M1+). A brief check from Intel users to see if these builds still work fine would be handy.

[schm1dtmac]

@Megamouse Had to kill the unit test/google test stuff you added to macOS arm64 CI a while back, it was locking up and breaking the arm64 builds for some reason starting yesterday (googletest update broke something? IDK).

EDIT: Apparently not googletest's fault, I re-ran builds from prior to the simple array unit tests being added and it built fine, that PR I suspect is causing some bother for me (and may also be linked to some crashes I thought were caused by this PR).