This progresses the goal of merging TaskProcessor and CommandQueue.
Moving the serial management out of RendererVk allows these classes
to have finer control over when thread synchronization locks happen.

Note: device lost handling seems untested currently.

Bug: b/172704839
Change-Id: I0cc61e1ffe41aad0b898d4146c8dbd08a2cebd3c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2525140
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>