AsyncRx.NET's Do operator overloads more prone to ambiguity than normal Rx.NET'

[idg10]

There are overloads of AsyncEnumerable.Do that accept an Action<Exception>. The problem with this is that is can lead to ambiguity with the one that accepts an Action<T>.

This has caused problems as we start to try to make the existing test suite for Rx.NET work on AsyncRx.NET.

Normal Rx.NET seems to avoid this by offering a more selective set of overloads. We should probably follow suit in AsyncRx.NET.