Add groundBuilder's import (#8522)
Add groundBuilder's import (#8522)

If we just copy&run the example without import the groundBuilder that will throw MeshBuilder exception.
Kesshi/Babylon.js,sebavan/Babylon.js,RaananW/Babylon.js,NicolasBuecher/Babylon.js,BabylonJS/Babylon.js,NicolasBuecher/Babylon.js,BabylonJS/Babylon.js,RaananW/Babylon.js,sebavan/Babylon.js,BabylonJS/Babylon.js,sebavan/Babylon.js,Kesshi/Babylon.js,Kesshi/Babylon.js,RaananW/Babylon.js,NicolasBuecher/Babylon.js