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.
