Refcount all GPU resources

Right now, only pl_buf_poll is refcounted, but there are a number of reasons it would be beneficial to extend this refcounting to every object type:

1. It would allow us to trivially write pl_tex_poll in the same way we currently have pl_buf_poll, which may help for interop with APIs that don't support semaphores.
2. It would allow us to free GPU resources as early as possible, rather than deferring the destruction to the latest command. By having e.g. pl_tex_destroy just deref the pl_tex, it will get freed automatically whenever no more commands use it.
3. It would allow us to move away from the assumption that command buffers can be sequentially ordered, i.e. moving towards a DAG representation of the command queues in the long-term. (With a refcount, the order of dereferencing does not matter)

added enhancement good first issue vulkan labels

mentioned in commit 781b2b06

Added this for pl_tex, which is the only resource I see really benefiting from this. (pl_pass lazy destruction is a non-issue). Decided not to add pl_tex_poll just yet because it makes me uncomfortable. I'd need to have a motivating use case for it.

If we ever move to a DAG-like command scheduler, we can add the remaining two non-refcounted resources trivially.

closed