I've added a wrapper struct in order to get around too many arguments warning.
It captures &dyn Repo as CommitTemplateLanguage would do. OTOH, &Ui is passed
by argument because the caller might need &mut Ui after the renderer object was
configured.
What make rebase_to_dest_parent a good candidate for jj_lib::rewrite module:
- It is used both in obslog and interdiff. It's a sign that it may be moved to a lower layer
- CommandError is returned by converting from TreeMergeError. Not explicitly.
- It only use jj_lib::rewrite fonctions.