Mainly to implement `GetResourceAllocationInfo1()`, but we can introduce `Device7` without much risk of apps failing on unimplemented methods, and doing that separately would conflict with `GetResourceAllocationInfo1()`.
-- v2: vkd3d: Implement GetResourceAllocationInfo1(). tests/d3d12: Add tests for GetResourceAllocationInfo1(). vkd3d: Support multiple descriptions in GetResourceAllocationInfo(). tests/d3d12: Test multiple descriptions in test_resource_allocation_info(). vkd3d: Add ID3D12Device7 interface stubs. vkd3d: Add ID3D12Device6 interface stub.