rebase: add --confirm option This feature adds a functionality in rebase to confirm before applying changes. When there is no conflict and user confirm to apply actions, we just finish the unfinished rebase. But when there is a conflict and user confirm to apply actions then we can't just finish rebasing using rbsrt._finishrebase() because in-memory merge doesn't support conflicts, so we have to abort and run on-disk merge in this case. And if user doesn't confirm to apply actions then simply abort the rebase. Differential Revision: https://phab.mercurial-scm.org/D3870