Fix a number of small memory leaks in the Metal backend. Unreleased blit
shader objects and temporary textures addressed. Static memory manager
modified to defer creation until use. Added reference count tracker to
shared memory manager across contexts, such that cached memory allocations
will be released if all contexts are destroyed and re-initialized.
Authored by Apple: Michael Parkin-White
Ref T96261
Reviewed By: fclem
Differential Revision: https://developer.blender.org/D16415
Metal: MTLVertBuf implementation and support for texture creation from vertex buffers.
Authored by Apple: Michael Parkin-White
Reviewed By: fclem
Maniphest Tasks: T96261
Differential Revision: https://developer.blender.org/D15452
