The current implementation generates entry points for GL up to
version 3.1. Will need to support later versions for some apps.

Bug: angleproject:3698
Change-Id: Ic44d07b12a9eeeceb8cd98dd9c44652dca728dc0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1700572
Commit-Queue: Clemen Deng <clemendeng@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>