Update pretty printing for new 'Bound' and 'NomVar'.
Update pretty printing for new 'Bound' and 'NomVar'.

We now have source language name information in the DeBruijn terms, so
we can print something closer to the preterms when printing the typed
terms.

The names printed for DeBruijn vars still have potentially unnecessary
numeric suffixes added for uniqueness; these can be eliminated as
described in the comments.

spire/spire