Add support for remaining OpenCL 1.2 enqueue commands to front end
and pass-through back end.

Bug: angleproject:6015
Change-Id: Iab650e42d51e2105dc826088d3606c56d5cd0fd5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2944966Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: John Plate <jplate@google.com>