We can consolidate exposing these extensions in initCaps. Otherwise
we have to maintain the lists in every Renderer back-end.

Also do the same treatment for select egl::Display extensions.

BUG=angleproject:1319

Change-Id: I529dd120c6d2cdbb789bd9dd20491e796e97f3f6
Reviewed-on: https://chromium-review.googlesource.com/345914Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>