[skif] Update Blur imagefilter to use new bounds APIs

Bug: b/294100597
Change-Id: I1b4f6af567fb23b4a0782f9e97696439e5930261
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/733457
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
10 files changed