Add two new validation functions: ValidateUniform1iv() and
ValidateProgramUniform1iv().
No functional change, just hooks for additional sampler uniform validation
that will come later.
This also lets us skip the sampler test in the more generic
ValidateUniformValue() function.

BUG=angleproject:1711

Change-Id: Ia6b7b45c22c2cf4b49a55fac62410ca4c91d09f4
Reviewed-on: https://chromium-review.googlesource.com/436884Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>