This is the asynchronous version of M:System.Data.Common.DbConnection.Open. The cancellation token can optionally be honored.The default implementation invokes the synchronous call and returns a completed task. The default implementation will return a cancelled task if passed an already cancelled cancellationToken. Exceptions thrown by Open will be communicated via the returned Task Exception property.Do not invoke other methods and properties of the DbConnection object until the returned Task is complete.