[svg] Implement feImage

Also cleaned up the IsFilterEffect() predicate a bit.

Bug: skia:10841
Change-Id: I8ef827df42d5d60cf06e74870191de7f27612376
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/404218
Commit-Queue: Tyler Denniston <tdenniston@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
diff --git a/modules/svg/include/SkSVGNode.h b/modules/svg/include/SkSVGNode.h
index 8079c85..9ca1b33 100644
--- a/modules/svg/include/SkSVGNode.h
+++ b/modules/svg/include/SkSVGNode.h
@@ -33,6 +33,7 @@
     kFeDistantLight,
     kFeFlood,
     kFeGaussianBlur,
+    kFeImage,
     kFeMorphology,
     kFeOffset,
     kFePointLight,