Generate OpTypeSampledImage deterministically (#446)
Generate OpTypeSampledImage deterministically (#446)

Fixes #442

* Add a new unique vector that tracks image types
  * iterate through this vector instead of the image type map so that
  OpTypeSampledImage instructions are generated deterministically
google/clspv,google/clspv,google/clspv,google/clspv,google/clspv