#2264:

While working on #2452 I found I would like to extend this to passes as well: once a pass has ended, attempting to encode commands generates a validation error instead of marking the encoder as invalid.

This is nice because it means invalid commands can just "locally" make their pass encoder invalid instead of needing a way to reach out to the top-level encoder and make that invalid after endPass() has already happened.

In #2452 I changed the behavior and then forgot about it before landing it.

So we have to determine: when you endPass() or encode a pass command after a pass has ended:

1. (Before 2452) silently make the top-level encoder invalid? (This is exceptional if you consider validity to be local to the pass, and in 2452 I've made it so pass commands don't otherwise affect the top-level encoder)
2. (After 2452) generate a GPUValidationError? (This is exceptional if you consider "pass must be open" to be just another validation rule rather than a special rule in encoding pass commands)