[google_maps_flutter_web] Issue 64073 implement my location

[Zubii12]

Implement my location button, add blue dot location

Fixes flutter/flutter#64073

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[gemini-code-assist]

Code Review

This pull request adds support for the 'My Location' button and current location tracking in the Google Maps Web plugin by introducing MyLocationController, MyLocationButton, and a mockable GeolocationApi. The review feedback highlights several critical issues, including potential resource and memory leaks from uncleared geolocation watches and map event listeners, runtime crashes in non-secure contexts due to unchecked geolocation support, and unsafe force-unwrapping of _markersController. Additionally, the feedback suggests using relative asset paths instead of web.window.location.href, triggering the location button's loading animation, preventing duplicate CSS injections, adding accessibility attributes, and improving double literal readability.

[gemini-code-assist]

In non-secure contexts (HTTP) or browsers where Geolocation is not supported, web.window.navigator.geolocation is undefined / null. Accessing it directly and calling methods on it will throw a runtime TypeError and crash the application. Check if geolocation is supported before attempting to use it.

class WebGeolocationApi implements GeolocationApi {
  web.Geolocation? get _geolocation {
    try {
      return web.window.navigator.geolocation;
    } catch (_) {
      return null;
    }
  }

  @override
  int watchPosition(
    void Function(double latitude, double longitude) onSuccess,
    void Function(dynamic error) onError,
  ) {
    final geolocation = _geolocation;
    if (geolocation == null) {
      onError('Geolocation is not supported or not available in this context.');
      return 0;
    }
    return geolocation.watchPosition(
      (web.GeolocationPosition location) {
        onSuccess(location.coords.latitude, location.coords.longitude);
      }.toJS,
      (web.GeolocationPositionError error) {
        onError(error);
      }.toJS,
      web.PositionOptions(),
    );
  }

  @override
  void getCurrentPosition(
    void Function(double latitude, double longitude) onSuccess,
    void Function(dynamic error) onError, {
    int timeoutMs = 30000,
  }) {
    final geolocation = _geolocation;
    if (geolocation == null) {
      onError('Geolocation is not supported or not available in this context.');
      return;
    }
    geolocation.getCurrentPosition(
      (web.GeolocationPosition location) {
        onSuccess(location.coords.latitude, location.coords.longitude);
      }.toJS,
      (web.GeolocationPositionError error) {
        onError(error);
      }.toJS,
      web.PositionOptions(timeout: timeoutMs),
    );
  }

  @override
  void clearWatch(int watchId) {
    _geolocation?.clearWatch(watchId);
  }
}

[Zubii12]

web.Geolocation is not null