Working on enhancing worker thread to completely own primary command
buffers. This will include not only processing SCBs from main thread
into a primary, but also submitting those command buffers to the queue.

The CommandProcessor is a vk::Context so it can handle errors in the
worker thread. When the main thread submits tasks to the worker
thread it also syncs any outstanding errors from the worker.

Include asynchronousCommandProcessing feature that will control
whether the worker thread task does it's work in parallel or not. If
false, we wait for the thread to complete it's work before letting the
main thread continue.  If true, the thread can execute in parallel with
the main thread.

Bug: b/154030730
Bug: b/161912801
Change-Id: I00f8f013d6cbb2af12a172c4f7927855db2f0ebf
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2328992
Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>