[core] Submission doesn't check for destroyed textures

[jimblandy]

wgpu_core::device::queue::Queue::submit calls validate_command_buffer, which checks for destroyed buffers, but it doesn't perform any analogous check on textures. Should it?

[sagudev]

It should per spec:

If any of the following requirements are unmet, generate a validation error, invalidate each GPUCommandBuffer in commandBuffers and return.
For each of the following types of resources used by any command in any element of commandBuffers:
...
GPUTexture t
t.[[destroyed]] must be false.
...

[jimblandy]

I'll mark this P1 for now, because it seems like freeing the texture too early could cause problems. But if it's not a crasher, then we can lower the priority to P2.