Instead of allocating one large descriptor pool and hoping we never run
out of descriptors, allocate small ones dynamically, so we know we never
run out.
Test incldued, though the test doesn't fail in CI, because llvmpipe
doesn't care about pool size limits. It does fail on my AMD though.
A fun side note about that test is that the GL renderer handles it best
in normal operationbecause it caches offscreens per node and we draw the
same node repeatedly.
But, the replay test expands them to duplicated unique nodes, and then
the GL renderer runs out of command queue length, so I had to disable
the test on it.
9e27acb0a6