The added tests check that using textureSize() and texelFetch() on
textures with a fixed point format return expected results. texelFetch
is also covered for integer format textures.

dEQP GLES 3.1 tests also cover a variety of multisampled array texture
formats.

BUG=angleproject:2775
TEST=angle_end2end_tests, angle_deqp_gles31_tests

Change-Id: I99b422e24b39e3563ed72f0fb85c9c1907df807d
Reviewed-on: https://chromium-review.googlesource.com/1196521
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>