These two features are heavily used in the
functional.depth_stencil_clear.* dEQP tests.

Enable a bunch of color/depth/stencil clear tests, however there is
still 2 tests in particular that are giving me trouble. I will work
on them separately in a subsequent change.

Bug: angleproject:2443
Bug: angleproject:2455

Change-Id: Ic93420c7b525b424e9641f78265e264ddb163ab1
Reviewed-on: https://chromium-review.googlesource.com/996035
Commit-Queue: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>