[sksg] 4x4 matrix support

Refactor the scene graph transform hierarchy to support 4x4 matrices:

  * rename current Transform to TransformEffect (operates as a render tree effect)
  * introduce a new Transform abstract base class, to replace current Matrix
  * refactor existing Matrix as a Transform specialization
  * introduce a new Matrix44 Transform specialization
  * refactor the existing composition helper (ComposedMatrix) as Concat,
    a Transform specialization (using composition instead of Matrix inheritance)

Change-Id: Ic3c1b499e10a0a229a7a76d4bef3dbc6a8b49194
Reviewed-on: https://skia-review.googlesource.com/c/182666
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/modules/sksg/samples/SampleSVGPong.cpp b/modules/sksg/samples/SampleSVGPong.cpp
index 15a1afe..a849add 100644
--- a/modules/sksg/samples/SampleSVGPong.cpp
+++ b/modules/sksg/samples/SampleSVGPong.cpp
@@ -144,7 +144,7 @@
             SkMatrix::MakeRectToRect(SkRect::MakeWH(1, 1),
                                      SkRect::MakeIWH(this->width(), this->height()),
                                      SkMatrix::kFill_ScaleToFit));
-        auto root = sksg::Transform::Make(std::move(group), fContentMatrix);
+        auto root = sksg::TransformEffect::Make(std::move(group), fContentMatrix);
         fScene = sksg::Scene::Make(std::move(root), sksg::AnimatorList());
 
         // Off we go.