Translate the extension's internal formats and formats to values valid
in core ES 3.0.

Bug: angleproject:4655
Change-Id: Ie47d01fb2ebca7bab5058812c9f4217523f784a0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2213262
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>