Wrap NV_path_rendering API with GrGLPathRendering

Adds a GrGLPathRendering class that wraps the NV_path_rendering
extension and manages its various API versions. It also provides
backup implementations when certain NVpr methods from later API
versions are not present on the current system.

BUG=skia:
R=bungeman@google.com, bsalomon@google.com, kkinnunen@nvidia.com

Author: cdalton@nvidia.com

Review URL: https://codereview.chromium.org/444223002
14 files changed