Add EGL_FEATURE_OVERRIDES_ENABLED_ANGLE and
EGL_FEATURE_OVERRIDES_DISABLED_ANGLE to submit lists of strings naming
the features that should be overridden (either enabled or disabled) on
display creation.

Bug: angleproject:1621
Change-Id: I4bb75c5dbab0e3b701a72069c38f8c60ecfffad2
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1646595
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>