This saves code duplication and makes the sampler validation a bit
simpler. In the future we might be able to use it to replace the
custom D3D logic for caching sampler info, but this relies on
some shader-specific non-merged data.

This also introduces some code duplication in Uniform1iv.

BUG=angleproject:1685

Change-Id: I258607a21886ca20766607bddf958cd511fac3f1
Reviewed-on: https://chromium-review.googlesource.com/426781Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>