fix: copy handler migrated to latest api (#192)

* fix: copy handler migrated to latest api

* flutter analyze

* code formatted

* fix: test added for copy handler

* more test added for copy handler

* fix:write test for copy handler

* text added for html to nodes

* fix: added more test for html encoder

* fix:removed unused imports

* fix: copyhandler collapse state test added

* added direct event handler in test

* flutter analyze

* revert changes in example.json

test/new/infra/testable_editor.dart

@@ -97,6 +97,12 @@ class TestableEditor {
     );
   }
 
+  void initializeWithDocment(Document document) {
+    _editorState = EditorState(
+      document: document,
+    );
+  }
+
   Future<void> dispose() async {
     _ime = null;
     // Workaround: to wait all the debounce calls expire.