GPU Upload Heap & UMA.

[blueskythlikesclouds]

• Vulkan doesn't appear to have an explicit way to check for UMA. We can check for VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT | VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT memory type combination, but this also passes for my NVIDIA card, supposedly due to ReBAR being enabled? Needs to be verified.
• GPU upload heaps supposedly can be reported as unsupported on UMA devices on old Windows versions, even if they are functionally the same. Falling back to UPLOAD does not work either, as they are restricted to GPU readonly states by the specification. This can be bypassed by creating a CUSTOM buffer with same properties as UPLOAD, but D3D12MA requires you to create a custom pool for that.

EDIT: Fixes #1076.