Enable point sprites in StateManagerGL. Fixes: * conformance/rendering/point-size.html * conformance/rendering/point-with-gl-pointcoord-in-fragment-shader.html * PointSpritesTest * particle_system sample BUG=angleproject:883 Change-Id: Idb3352fa916cf08817496f0a8425c95ece9bfa49 Reviewed-on: https://chromium-review.googlesource.com/275860 Reviewed-by: Zhenyao Mo <zmo@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>