Fix caching problem when computing implicit scopes
Fix caching problem when computing implicit scopes

Caches were set when information was not complete yet. Problem was
exhibited by missing some `eqName` implicits when adding safe equality
for Name.

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