This brings the grammar closer to the GLSL ES 3.10 spec.

Some corner cases related to handling unsized arrays are fixed.

BUG=angleproject:2125
TEST=angle_unittests, angle_end2end_tests

Change-Id: I9bcf87b17b97da0e2ec2954d32037c272fde3080
Reviewed-on: https://chromium-review.googlesource.com/738233Reviewed-by: Jamie Madill <jmadill@chromium.org>