refactor(useNodesData): improve selector equality function (#3976)

* improved selector equality function for useNodesData

* fixed selector & useNodesData example

* added shallow-node-data as system function

packages/system/src/utils/index.ts

@@ -7,3 +7,4 @@ export * from './marker';
 export * from './node-toolbar';
 export * from './store';
 export * from './types';
+export * from './shallow-node-data';