Added NV/OES suffixes to relevant Extensions members.

Bug: angleproject:3104
Change-Id: Ia1798157086230bde8d11c6fcb4fe93211e996ab
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2013168Reviewed-by: Alexis Hétu <sugoi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>