src/parser/floc-proto.lisp: Add `enclosing-condition-with-location-type'.

src/parser/floc-proto.lisp: Add `enclosing-condition-with-location-type'.

Split out the piece of `make-condition-with-location' which figures out
the appropriate subclass of `condition-with-location' to use to wrap a
given condition so that it can be extended more easily.