Add AMD allocator to D3D12 backend.

Adds base class GrD3DAlloc and GrD3DMemoryAllocator, and a reference
to a GrD3DMemoryAllocator in GrBackendContext and a reference to a
GrD3DAlloc in GrD3DTextureResourceInfo. Internally, we override this
base class to define the AMD memory allocator.

Change-Id: I033924b0247ea330969b1398f25985e7a84aec11
Bug: skia:9935
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/317243
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
16 files changed