GPU: Prevent null dereference if expected binding is missing

[thatcosmonaut]

In SDL GPU we defer resource bind calls to draw call time by maintaining an array of resources that the client has requested to bind. The Vulkan and D3D12 backends were storing resource pointers in these arrays. But if the client forgets to bind a resource that the pipeline expects, we end up dereferencing a null pointer. To prevent this, instead of storing the client handles to perform bindings, let's store the actual resource handles that the backend expects, and we can zero out the array of those handles when the pass is done. We can then easily log when an expected binding is missing.

This will end up spamming a lot of errors if the client forgets to bind something. Maybe there's a better way to handle this? On the other hand it's a serious error that should be fixed immediately by the client.

Resolves #13128

[thatcosmonaut]

Restructured the checks so that we can just record keep in gpu.c and avoid the overhead when not in debug mode.