This change will make it possible for context classes to
access multiple versions, e.g. GL version and GLES version

Bug: angleproject:3661
Change-Id: I77a33d1c3ea3bffe94c64deb272219bbda1725a4
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1689023
Commit-Queue: Clemen Deng <clemendeng@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>