Investigate MTLBinaryArchive to see if we can get the "pipeline cache" supported with the Metal backend

Vulkan, OpenGL, and D3D11 all have support for the pipeline cache blob save/load. (granted, with GL and D3D11 this is sort of simulated with program binaries and the collected DX bytecode binaries) We should check if Metal has a way to make this work, via MTLBinaryArchive.

With this in place we'd have the necessary support realize the improvements outlined in QTBUG-103802 on all platforms.