[canvaskit] Add docs/types for Paint and Filters/Effects

This also includes matrices (which I'm reminded I want to test with
TypedArrays and make optional).

Bug: skia:10717
Change-Id: I0f6565a46b766c1f81c28dfc1229d403bff32e69
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/321118
Reviewed-by: Nathaniel Nifong <nifong@google.com>
diff --git a/modules/canvaskit/interface.js b/modules/canvaskit/interface.js
index 635ce28..14cb591 100644
--- a/modules/canvaskit/interface.js
+++ b/modules/canvaskit/interface.js
@@ -551,7 +551,7 @@
     return m;
   }
 
-  // concat returns a new SkColorMatrix that is the result of multiplying outer*inner;
+  // concat returns a new SkColorMatrix that is the result of multiplying outer*inner
   CanvasKit.SkColorMatrix.concat = function(outer, inner) {
     var m = new Float32Array(20);
     var index = 0;