Geo add the ability to get a reference to the map instance

Is your feature request related to a problem? Please describe 🙏

It might happen in some cases that you directly want to interact with the map instance. Right now the only way to get this instance is through the event listeners on the markers. It would be nice to provide it as soon as the map is instantiated.

Describe the solution you’d like 🤔

We can trigger an event once the map is instantiated.

search.addWidget(
  instantsearch.widgets.geoSearch({
    container: "#geo-search-container",
    googleReference: window.google,
    events: {
      onMapCreated: instance => {
        // Do something with the instance
      }
    }
  })
);

Additional context

See https://github.com/algolia/instantsearch.js/issues/2778#issuecomment-411552188

[samo012]

For anyone still wondering, a reference to the map is passed in the events from builtInMarker and customHTMLMarker.

[bobylito]

@bobylito then it would be undefined before mounted right?

Probably indeed 😅 . Other idea: what about having a method on the widget instance that returns a promise of the map?