Move dune-typetree to dune-common
This was decided on the 2020 dev meeting:https://dune-project.org/community/meetings/2020-02-devmeeting/.
This issue if for managing the transition.
This was decided on the 2020 dev meeting:https://dune-project.org/community/meetings/2020-02-devmeeting/.
This issue if for managing the transition.