This change adds Collabora, Ltd. to the AUTHORS file as described in the
ContributingCode guide.
Also adds Collabora, Ltd. and myself to CONTRIBUTORS.

Bug: angleproject:5516
Change-Id: Ie24ef8ec01720d9d207d36c4a4c21fab96d08dcd
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2690949Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>