Expose the new style property of GoogleMap with version 2.6

[giorgio79]

Previously, we could call

 PlacePicker(
        onMapCreated: (mapController) {
          mapController.setMapStyle(globals.gMapsMonochrome);
        },

Now as per https://pub.dev/packages/google_maps_flutter/changelog#260

"Adds style to the GoogleMap widget constructor. This allows setting the map style during creation, avoiding the possibility of the default style being displayed briefly.
Deprecates GoogleMapController.setMapStyle in favor of setting the style via the new widget style parameter."

Eg if someone had a dark theme with Google Maps:
flutter/flutter#144524