endConnection method
Calls
`BillingClient#endConnection(BillingClientStateListener)`
(https://developer.android.com/reference/com/android/billingclient/api/BillingClient.html#endconnect
to disconnect a BillingClient
instance.
Will trigger the OnBillingServiceDisconnected callback passed to startConnection.
This triggers the destruction of the BillingClient
instance in Java.
Implementation
Future<void> endConnection() async {
return _hostApi.endConnection();
}