dispose method
void
dispose()
Implementation
void dispose() {
if (_disposed) return;
_detachNative();
_disposed = true;
_channel?.setMethodCallHandler(null);
_channel = null;
_mapReady = false;
_onMapLoaded = null;
_onMapClick = null;
_onCameraMove = null;
_onCameraMoveStart = null;
_onCameraIdle = null;
_onMarkerClick = null;
_onMarkerPopupToggle = null;
_pendingActions.clear();
}