Inline relevant parts of IntrospectableM2M

Inline relevant parts of IntrospectableM2M

Quoth ribasushi:

> The dependency is discouraged, and often outright dangerous from an
> architectural standpoint.  Having S::L explicitly depend on it, *just*
> for a test is silly, as the test-side can be accomplished with an ad-hoc
> override within the base test schema in the dist, which would result in
> IM2M not being installed for vast majority of users.