Move the source image into Context

This folds the source SkSpecialImage, that was previously passed in as
an argument to filterImage(), into the filtering Context. This allows
the Context to provide convenient access to backend properties that
are only accessible through the source image, but makes it clear in
calling code that the actual pixels of the source image are not needed.

IMO this improves readability in implementations that previously had
functions that would take a 'src' and an 'input' image, but would only
really process the input image's pixels.

Bug: skia:9282
Change-Id: I42437dcc6819e3d3882bff7851f9b16277a69f06
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/234578
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
32 files changed