This consolidates most of the command processor vs queue logic in one
place. It also has a number of incidental changes related to fences:

- syncs now do not store a shared fence. instead they call command
  apis to wait for a particular serial with a timeout. this is not
  yet fully implemented in CommandProcessor.
- surface swap history stores a serial instead of a fence. because
  the RendererVk class stores the command batches, we no longer have
  to do messy things with ContextVk.
- it is no longer possible to ask for a wait on a serial that isn't
  in the command queue.

Also adds mutex synchronization around the RendererVk methods.

Bug: angleproject:5217
Bug: b/172704839
Change-Id: I5faf0e24bb6ede79a927ab149b80bfa8baca4620
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2524548
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>