Create GrVkCopyPipeline class

This creates a special subclass of GrVkPipeline that we can use for doing
copies on draws. Currently this is not hooked into the system.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2353563003

Review-Url: https://codereview.chromium.org/2353563003
4 files changed