Implement shader compiler support for uint vectors.

Bug 19331817

Change-Id: Ib85c82f7490a5e48830fb496cddbb5aa6837dfb2
Reviewed-on: https://swiftshader-review.googlesource.com/2313
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>