Extra and discardable instrumentation of replace_late_bound_regions_in_fn_sig.
Instrument outset of construct_parameter_environment.
Fix #5121: Early/Late Bound related ICEs.

The problem was that we need to apply the substitution, so that the
formal lifetime parameters get replaced with (unifiable)
free-lifetimes that can actually be fed into the constraint solver.
Validate in `check_bare_fn` that function type has no early-bound lifetimes.