[svg] Implement feOffset filter

https://www.w3.org/TR/SVG11/filters.html#feOffsetElement

We should now be passing filters-felem-02-f W3C test.

Bug: skia:10841
Change-Id: I642cf3c8816b83bdf88066c55103e432ae9c9d5a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/354216
Commit-Queue: Tyler Denniston <tdenniston@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
6 files changed