Update typedef format

Author: JamesMcIntosh

packages/google_maps_flutter/google_maps_flutter/example/lib/place_marker.dart

@@ -29,7 +29,7 @@ class PlaceMarkerBody extends StatefulWidget {
   State<StatefulWidget> createState() => PlaceMarkerBodyState();
 }
 
-typedef Marker MarkerUpdateAction(Marker marker);
+typedef MarkerUpdateAction = Marker Function(Marker marker);
 
 class PlaceMarkerBodyState extends State<PlaceMarkerBody> {
   PlaceMarkerBodyState();

packages/google_maps_flutter/google_maps_flutter/lib/src/google_map.dart

@@ -8,7 +8,7 @@ part of google_maps_flutter;
 ///
 /// Pass to [GoogleMap.onMapCreated] to receive a [GoogleMapController] when the
 /// map is created.
-typedef void MapCreatedCallback(GoogleMapController controller);
+typedef MapCreatedCallback = void Function(GoogleMapController controller);
 
 /// A widget which displays a map with data obtained from the Google Maps service.
 class GoogleMap extends StatefulWidget {