fix(extra_fields): fixed bug where searchable dropdown dialog height couldn't be adjusted. Fixes #926

Author: danvick

packages/form_builder_extra_fields/lib/src/fields/form_builder_searchable_dropdown.dart

@@ -283,7 +283,7 @@ class FormBuilderSearchableDropdown<T> extends FormBuilderField<T> {
               key: ValueKey(state.value),
               // Hack to rebuild when didChange is called
               items: items,
-              maxHeight: 300,
+              maxHeight: maxHeight,
               onFind: onFind,
               onChanged: (val) {
                 state.requestFocus();