[D3D12/Vulkan] Simplify host GPU fence management

Replace the `SubmissionTracker`s with new `GPUCompletionTimeline`s with a
more unified interface (using a base class), and without the internal logic
for queue ownership transfers since that idea was scrapped during the
development of the `Presenter`.

Also use this fence management logic for GPU emulation, though without
architectural reworks for now, just on the bottom level.

Still very messy, but can be cleaned up in further GPU command processor
and presenter reworks.