Use the name "uniformLocationBindings" for location information set by
the API instead of "uniformBindings", which can be easily confused
with binding layout qualifiers that can be set for some types of
uniforms. Also use more straightforward names throughout the
indexUniforms function.

BUG=angleproject:1442

Change-Id: I47d504479b36def696305f060e9c9bd3de3ade48
Reviewed-on: https://chromium-review.googlesource.com/445236Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>