This gives the features the exact same name as the member variable.
It fixes a bunch of inconsistencies between the variable name and the
external string identifier.

Ideally these could be auto-generated from JSON.

Bug: b/172704839
Change-Id: Id75c01db544672234435c3dd727c927027b9236d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2524541Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>