fix: add loading=async to maps API url

The new parameter loading=async signals to the API that we're not relying on the load-event of the script tag to determine the maps API status and allows the maps API to do some backward-incompatible performance-optimizations.

src/libraries/google-maps-api-loader.ts

@@ -121,7 +121,10 @@ export class GoogleMapsApiLoader {
           urlParams.set(urlParamName, value);
         }
         urlParams.set('libraries', library);
+        urlParams.set('loading', 'async');
         urlParams.set('callback', '__googleMapsCallback__');
+
+        scriptElement.async = true;
         scriptElement.src = MAPS_API_BASE_URL + `?` + urlParams.toString();
 
         window.__googleMapsCallback__ = () => {