Re-land "converted GrCircleBlurFragmentProcessor to sksl"

This reverts commit 818ac5a00dfd570d2b291b7524a70ecd4ef55770.

Bug: skia:
Change-Id: I9bd8a06bd2dbb40bd261d64d6d04daf864bc00a5
Reviewed-on: https://skia-review.googlesource.com/22075
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
14 files changed