Cleanup lambda lift
Cleanup lambda lift

1. Make clearer what markFree is supposed to do and get
   rid of `propagated` mode bit.
2. Harden copyParams so that we make sure corresponding
   parameters and fields are copied.

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