Upgrade gl2ext.h. Includes a new entry point needed for disjoint timer queries. This header is copied exactly from Khronos's official repo. We add one change so that we can include special ANGLE modifications in gl2ext_angle.h. Bug: angleproject:4433 Change-Id: I6c9cbdfa73ca3de052ff49c5ea91eb5e9a9ee699 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2080596 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>