The solution (after many false starts) is to change the behavior of
hsLTyClDeclBinders. The idea is that the locations of the names that
the parser generates should really be the names' locations, unlike
what was done in 17457791... But, when the renamer is creating Names
from the RdrNames, the locations stored in the Names should be the
declarations' locations. This is now achieved in hsLTyClDeclBinders,
which returns [Located name], but the location is that of the
*declaration*, not the name itself.