createOffer method
Implementation
@override
Future<RTCSessionDescription> createOffer(
[Map<String, dynamic>? constraints]) async {
final args = constraints != null ? [jsutil.jsify(constraints)] : [];
final desc = await jsutil.promiseToFuture<dynamic>(
jsutil.callMethod(_jsPc, 'createOffer', args));
return RTCSessionDescription(
jsutil.getProperty(desc, 'sdp'), jsutil.getProperty(desc, 'type'));
}