moved visualDensity to named parameter.

Author: Sumit258000

lib/src/fields/form_builder_checkbox_group.dart

@@ -26,9 +26,10 @@ class FormBuilderCheckboxGroup<T> extends FormBuilderFieldDecoration<List<T>> {
   final OptionsOrientation orientation;
 
   /// Creates a list of Checkboxes for selecting multiple options
-  FormBuilderCheckboxGroup(this.visualDensity, {
+  FormBuilderCheckboxGroup( {
     super.key,
     required super.name,
+    this.visualDensity,
     super.validator,
     super.initialValue,
     super.decoration,