Track cross-queue vulkan buffer dependencies
We do this for images, but not for buffers - the assumption so far was that buffers wouldn't need cross-queue dependencies. However, this assumption may have changed with the introduction of texture format emulation.
We might get a performance boost from leveraging the DMA engine to do the TEX_TRANSFER -> TEXEL_UNIFORM
buffer copy, but this requires the texel buffer to undergo TRANSFER->COMPUTE transition, which our current buf_barrier
infrastructure is incapable of dealing with.
We could probably just copy/paste the vk_signal
abstraction here, (i.e. use it for buffers in addition to images), although I'm worried about incurring unnecessary events for buffers as well.