Add: Clipboard toolbar buttons

lib/src/editor/raw_editor/raw_editor.dart

@@ -31,9 +31,7 @@ class QuillRawEditor extends StatefulWidget {
             configurations.maxHeight == null ||
                 configurations.minHeight == null ||
                 configurations.maxHeight! >= configurations.minHeight!,
-            'maxHeight cannot be null') {
-    configurations.controller.readOnly = configurations.readOnly;
-  }
+            'maxHeight cannot be null');
 
   final QuillRawEditorConfigurations configurations;