[svg] Implement feMorphology filter

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

Bug: skia:10841
Change-Id: I0b0028fb815c490670f9f1e888770efb194a8f3b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/356107
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Tyler Denniston <tdenniston@google.com>
6 files changed