Give the ability to reset the last config #71
Description
The TestWireAdapterTemplate exposes a getLastConfig method but no way to reset it.
So for some tests where we want to ensure the wire was not called for some functional reasons, we should add them as first tests into the test file and ensure the wire is not called first on another file.
Ideally we should be able to give an easy way to reset any last config (classic, Lds, Apex) without hacking the internal implementation (we could set to null the static field _lastConfig but it means we know the internal implementation)