Validate SamplerFormat We weren't validating sampler formats in ProgramExecutable validation. Bug: chromium:1273661 Change-Id: Ida0c67c0c7169ea3f47ceb2d433bee17012a7e5e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3312717 Reviewed-by: Charlie Lao <cclao@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Lingfeng Yang <lfy@google.com>