Reland (x2) Skwasm overlay optimizations (#56067)

This is an attempt to reland #55468

We now defer actually drawing the pictures until the build of the layer slices, so that we can calculate an accurate `cullRect` for the picture recorder

This also contains a further optimization for the "simple" rendering case (no platform views) where we don't actually do any unnecessary occlusion calculations.

Author: eyebrowsoffire

lib/web_ui/lib/src/engine/color_filter.dart

@@ -135,4 +135,7 @@ class EngineColorFilter implements SceneImageFilter, ui.ColorFilter {
         return 'ColorFilter.srgbToLinearGamma()';
     }
   }
+
+  @override
+  Matrix4? get transform => null;
 }