Multi-GPU Resource Transfer

[Syncaidius]

Implement support for transferring resources between GraphicsDevice instances:

GraphicsResource.TransferTo(params GraphicsDevice[] device)

Scenarios where this may be needed:

• Transferring AI pathfinding compute results from a secondary GPU which need to be used on the primary GPU
• Textures generated on a secondary GPU that need rendering on the primary GPU.

Also consider if resource sharing can be implemented. ReBAR may also improve performance of sharing/transfering, by allowing the CPU to copy directly from one GPU's VRAM to another.