Descriptor pools were never discarded, leading to out of memory issues
when running for a long time. This PR discards used descriptor pool when
the render graph is submitted to the device.
- Detected that to descriptor sets could be uploaded multiple times
however once was always empty.
- When render graph is flushed all descriptor pools are discarded.
- Improved debugging of discard pools.
Pull Request: https://projects.blender.org/blender/blender/pulls/137521
5102f33ef9