Return target rect for SkPictureImageFilter forward bounds mapping

When mapping bounds in the forward direction, return the target rect of
the picture (fCropRect). This matches the behavior of SkImageSource
which can be considered to be semantically similar.

Bug: skia:10744
Change-Id: Ief213a847041ea6b276b2e7493e49db01715eda9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/319616
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
2 files changed