Multi-GPU Support

[Syncaidius]

Support for adding additional GPUs to task pools, so that they can be used to offload secondary compute or render tasks. For example, pathfinding/AI or texture generation tasks.

A mechanism may also need to be implemented to simplify duplicating, copying or transferring resources between GPUs, since resource cannot be directly shared between different GPUs.

A mechanism may also need to be provided for specifying which types of tasks each additional GPU is allowed to process, as a developer (or user) may want to assign lower priority tasks to less powerful GPUs.

This will rely on:

• Vulkan - Multi-context support #119
• DX12 - Multi-GPU support - Use secondary GPUs to offload compute or geometry streaming tasks #175
• [DX11] Deferred Context Support #53

[Syncaidius]

Implemented initial support for this in 7a9c51b