Rename SkXfermodeImageFilter to SkBlendImageFilter

Also deletes the old header under the deprecated name.

Bug: skia:11230
Change-Id: Iac42d2b980d3306a544077719ca62903a673210a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/368242
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
6 files changed