slant colorfilter away from filterSpan4f

rename to make it easy to delete any impl that also had onAppendStages...
i.e. rename to make it clear that it is just an impl trick for rasterpipeline.

Bug: skia:
Change-Id: If3c3b2811eff12d399cdf7a77552c01e72c06996
Reviewed-on: https://skia-review.googlesource.com/18234
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
16 files changed