We have this information stored in the front-end sampler bindings.
This solves sampler uniform query across the various back-ends.

Turns on a bunch of uniform_api dEQP tests.

Bug: angleproject:2612
Change-Id: If8752a26438595ad103598369df360e2f5e12d53
Reviewed-on: https://chromium-review.googlesource.com/1101572
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>