This reworks how host<->device synchronization works on the Vulkan
backend. Instead of "protecting" resources with a fence and signalling
these as free when the fence is known to be signalled by the host GPU,
use timeline semaphores.
Vulkan timeline semaphores allow use to work on a subset of D3D12
fences. As far as we are concerned, timeline semaphores are a value set
by the host or the device that can be waited by either of them.
Taking advantange of this, we can have a monolithically increasing
atomic value for each submission to the graphics queue. Instead of
protecting resources with a fence, we simply store the current logical
tick (the atomic value stored in CPU memory). When we want to know if a
resource is free, it can be compared to the current GPU tick.
This greatly simplifies resource management code and the free status of
resources should have less false negatives.
To workaround bugs in validation layers, when these are attached there's
a thread waiting for timeline semaphores.
All drivers (even Intel) seem to have a device local memory type that is
not host visible. Remove this flag so all devices follow the same path.
This fixes a crash when trying to map to host device local memory on
integrated devices.
Introduce a default buffer getter that lazily constructs an empty
buffer. This is intended to match OpenGL's buffer 0.
Use this for disabled vertex and uniform buffers.
While we are at it, include vertex buffer usages for staging buffers to
silence validation errors.
The job of this abstraction is to provide staging buffers for temporary
operations. Think of image uploads or buffer uploads to device memory.
It automatically deletes unused buffers.
