Fix #13140: 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.

Also, refactor code os that substitution for `check_item` and
`check_method`, moving both down the control flow into `check_bare_fn`.

----

Finally, there was another (similar) spot where we needed to
substitute early-bound lifetimes when invoking an object method of a
trait.
Fix Repr impl for method::Candidate to include the method_ty.
Add test using early-bound lifetimes in trait generic parameters.
auto merge of #13157 : pnkfelix/rust/fsk-iss13140, r=nikomatsakis

r? @nikomatsakis

Fix #13140

Includes two fixes, and a semi-thorough regression test.

(There is another set of tests that I linked from #5121, but those are sort of all over the place, while the ones I've included here are more directly focused on the issues at hand.)