Fix findMember of SuperType
Fix findMember of SuperType

It used to return the joint denotation, but the correct
answer is the denotation of the symbol in the joint denotation
as seen from the super prefix.

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