Auto merge of #1162 - msiglreith:core_merge, r=kvark
Auto merge of #1162 - msiglreith:core_merge, r=kvark

Migrate low level core API changes to core.

Add Surface, Instance, Swapchain, CommandQueue, QueueFamily and Adapter traits to core from corell.

The backends would need updates later-on. The dx12ll and vulkanll backends can be used for reference.
After the backend changes, the window crates shouldn't be needed anymore and replaced by the `Surface` and `SwapChain` parts.

Open question would be the support for other windows like SDL and glfw, because the current surface trait uses an associated window type.

ColinKinloch/gfx,davll/gfx,ColinKinloch/gfx,gfx-rs/gfx-rs,JohnColanduoni/gfx,tanderegg/gfx,tanderegg/gfx,JohnColanduoni/gfx