Allows setting/resetting multiple bits to be coalesced into one
operation.

Bug: angleproject:5528
Change-Id: Ibf2dff8c81441a75c268d95066d23da1b2a3c810
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2678885
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>