This PR adds recycling of descriptor pools. Currently descriptor pools
are discarded when full or context is flushed. This PR allows
descriptor pools to be discarded for reuse.
It is also more conservative and only discard
Descriptor pools when they are full or fragmented.
When using the Vulkan backend a small amount of descriptor memory can leak. Even
when we clean up all resources, drivers can still keep data around on the
GPU. Eventually this can lead to out of memory issues depending on how
the GPU driver actually manages descriptor sets.
When the descriptor sets of the descriptor pool aren't used anymore
the VKDiscardPool will recycle the pools back to its original VKDescriptorPools.
It needs to be the same instance as descriptor pools/sets are owned by
a single thread.
Pull Request: https://projects.blender.org/blender/blender/pulls/144992
e24e58f293