Fix: #1366, constant adaptation
Fix: #1366, constant adaptation

Fix: #1366. Constant adaptation did not work if the
expected type was an as yet uninstantiated type variable.

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