Add GrGLInterface support for sampler objects and GrGLCaps detection.

BUGL skia:8471

Change-Id: If67dbbcdca2d3130f6e10720c052c55a3b16482f
Reviewed-on: https://skia-review.googlesource.com/c/162561
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
8 files changed