[Web] Fix pointer binding (flutter#14378)

Refactors pointer_binding, fixes a few issues related to the pointer data converter in Web, and adds a number of tests for all three adapters.

Author: dkwingsmt

lib/web_ui/lib/src/engine/dom_renderer.dart

@@ -411,7 +411,7 @@ flt-glass-pane * {
     glassPaneElement
         .insertBefore(_accesibilityPlaceholder, _sceneHostElement);
 
-    PointerBinding(this);
+    PointerBinding.initInstance(_glassPaneElement);
 
     // Hide the DOM nodes used to render the scene from accessibility, because
     // the accessibility tree is built from the SemanticsNode tree as a parallel