Track descriptor pool size, and fail if we smash them

When working on the 28_gltf sample, I loaded Sponza, which allocated 630+ descriptors of each type (limit was set to 512).
Turns out some drivers are fine with that, other will fail, but then allow as soon as you bump the size of any descriptor type.
(https://gitlab.freedesktop.org/mesa/mesa/-/issues/8411)
Also, vulkan validation layers don't catch this one.

It might be useful for bigwheels to check the pool allocation limits, and fail when we try to allocate more than we asked for, so we don't end up with a changing behavior depending on the hardware/API.