This merges the 'commandProcessor' and 'asyncCommandProcessing'
features into one new 'asyncCommandQueue' features.

Conceptually the command processor is asynchronous use of the
CommandQueue. This renaming updates the code to reflect the usage.

Bug: b/172704839
Change-Id: I1d7ca1187f802eed48823a01b57fb520527f2540
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2525144
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>