With this new approach, descriptor pools are decoupled from the
command list they are used with. Instead, the DXVK context takes
ownership of a single descriptor pool until it runs out of memory.
This reduces the amount of memory wasted for under-utilized pools
and should this reduce an application's memory footprint.
Fixes a few bottlenecks that were encountered in the Cascading Shadow
Maps demo from the Microsoft SDK. Performance is now slightly better
than wined3d with CSMT, MESA_NO_ERROR and mesa_glthread enabled.
