For consistency, call these ANGLE "features", a subset of which may be
workarounds. Also, whether the feature is enabled/disabled should be
publically visible as "status".

Bug: angleproject:1621
Change-Id: I0de90a932fbfe1fc9b59138153d616d29fa7268b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1643410Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>