[google_maps_flutter] Add onPointOfInterestTap support

[tenninebt]

Summary

• App-facing GoogleMap.onPointOfInterestTap API, example, and tests
• Depends on published google_maps_flutter_platform_interface 2.17.0 ([google_maps_flutter_platform_interface] Add onPointOfInterestTap support #12752)
• Depends on published platform implementations from [google_maps_flutter] Add onPointOfInterestTap platform implementations #12880 (Android / iOS sdk9+sdk10 / web)

iOS note: POI taps require google_maps_flutter_ios_sdk9 or google_maps_flutter_ios_sdk10. The default/frozen google_maps_flutter_ios package does not receive new features.

Part of #11872.

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• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making.
• All existing and new tests are passing.

[gemini-code-assist]

Code Review

This pull request adds support for tapping points of interest on the map in the google_maps_flutter package by introducing the onPointOfInterestTap callback, updating the map controller to listen to the platform stream, and adding relevant tests and example usage. The feedback suggests checking if the widget is mounted before invoking the onPointOfInterestTap callback to prevent calling callbacks on an unmounted widget.

[gemini-code-assist]

Since the map controller's stream subscriptions are disposed asynchronously (via _disposeController awaiting _controller.future), there is a small window during widget disposal where a platform event can still be received. To prevent calling callbacks on an unmounted widget (which could lead to setState being called after dispose in parent widgets), it is safer to check mounted before invoking the callback.

  void onPointOfInterestTap(PointOfInterestId pointOfInterestId) {
    if (!mounted) {
      return;
    }
    final ArgumentCallback<PointOfInterestId>? onPointOfInterestTap = widget.onPointOfInterestTap;
    if (onPointOfInterestTap != null) {
      onPointOfInterestTap(pointOfInterestId);
    }
  }

[stuartmorgan-g]

This doesn't need to be a new PR; once you update #11872 to reconcile it with what has landed, what is left will be just the app-facing portion, and it will already have reviews so will just need a final approval of the updated version.