Uniforms can now legally be used as indices in
OpenGL ES 3.0, so they now have to be handled
properly in the dynamic indexing analysis.

Change-Id: I971aa55edcbc73796c30e0acc99156b513a78b80
Reviewed-on: https://swiftshader-review.googlesource.com/3550Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>