View selection can happen in the vertex shader through the optional
feature VPAndRTArrayIndexFromAnyShaderFeedingRasterizer.

BUG=angleproject:2062
TEST=angle_end2end_tests

Change-Id: Iaf65685e04f828b0936295fea867f6f6cbe69bee
Reviewed-on: https://chromium-review.googlesource.com/628419
Commit-Queue: Martin Radev <mradev@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>