Break out GrGLAssembleInterface into a few files

one for GL, one for GLES, and one (soon) for WebGL

Bug: skia:8378
Change-Id: Ib13699b7432ed56cce99ac568840e5575bb4d2e5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201654
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
6 files changed