merge: show list of bids for each file in bid-merge in ui.debug()
Earlier, we were showing the list of bids only when we were ambiguously picking.
However, the cases where we unambiguously picked a side may not always be
correct and need to be fixed.
Having list of bids for all files will be helpful in debugging.
Differential Revision: https://phab.mercurial-scm.org/D8966