Add AnyRef bound to TASTy reflect types
Add AnyRef bound to TASTy reflect types

All implementations are and will always be AnyRefs. This also allows us
to use methods such as mapConserve on a List[Tree].

sjrd/dotty,lampepfl/dotty,sjrd/dotty,lampepfl/dotty,dotty-staging/dotty,lampepfl/dotty,dotty-staging/dotty,sjrd/dotty,som-snytt/dotty,dotty-staging/dotty,som-snytt/dotty,som-snytt/dotty,dotty-staging/dotty,sjrd/dotty,dotty-staging/dotty,lampepfl/dotty,sjrd/dotty,som-snytt/dotty,som-snytt/dotty,lampepfl/dotty