Rename existing 'Blend' enums/names to 'BlendFilter'.

Change-Id: I17c624e9145d7152f65695ca3ce4592a11bb09a2
Bug: skia:12080
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/418637
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
9 files changed