dispose method

Implementation

dispose() {
  if (_isDisposed) return;
  _isDisposed = true;
  _eventHandlerMap.clear();
  try {
    _webViewController.removeJavaScriptHandler(handlerName: _handlerName);
    _webViewController.dispose();
  } catch (e) {
    _onBoardLog?.call('dispose error: $e');
  }
}