Being able to sample from sampler2DRect using the "texture" function is required for Chromium on Mac.

Change-Id: Iea8970aaec29734a251bcfc19a03223d0ebfbc7e
Reviewed-on: https://swiftshader-review.googlesource.com/17572Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>