QmlDesigner: Search Assets Library folders recursively

Fixes: QDS-13497
Change-Id: I44f9645ca86d82be3ab2e2d7a14e952ecd44c418
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>

src/plugins/qmldesigner/components/assetslibrary/assetslibrarymodel.cpp

@@ -24,6 +24,7 @@ AssetsLibraryModel::AssetsLibraryModel(QObject *parent)
     : QSortFilterProxyModel{parent}
 {
     createBackendModel();
+    setRecursiveFilteringEnabled(true);
     sort(0);
 }