Create blurred RRect mask on GPU (rather than uploading it)

This CL doesn't try to resolve any of the larger issues. It just moves the computation of the blurred RRect to the gpu and sets up to start using vertex attributes for a nine patch draw (i.e., returning the texture coordinates)

All blurred rrects using the "analytic" path will change slightly with this CL.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2222083004

Committed: https://skia.googlesource.com/skia/+/75ccdc77a70ec2083141bf9ba98eb2f01ece2479
Review-Url: https://codereview.chromium.org/2222083004
9 files changed