This now also includes reworking the attribute which activates
Autofixture-style resolution upon an IServiceProvider.
This has now been renamed to WithAutofixtureResolutionAttribute.
The new/reworked attribute is composable with other Autofixture
attributes.
This refactor of integration test logic is to boost its
reusability. Moving some functionality to attributes &
customization classes means I can reuse elsewhere without
duplication.