create static method
Implementation
static Future<FlutterBaseInterstitial> create(String zoneId) async {
MethodChannel commconChannel = FlutterBidmadCommon().platform;
String channelName = await commconChannel.invokeMethod('initInterstitialChannel');
FlutterBaseInterstitial instance = FlutterBaseInterstitial._internal(channelName);
await instance._setAdInfo(zoneId);
return instance;
}