Cleanup implementation of Reposition
Cleanup implementation of Reposition

Trees now have sources that can be used directly without the need of `enclosingInlineds`
to track the current source. This new implemetation simply uses the tree positions
directly and does not need to keep the context in sync with the `enclosingInlineds`.

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