Fix two bugs in HRTB: 1. Categorize early-vs-late bindings on impls when constructing    generics, so that we don't add unnecessary region parameters. 2. Correct the DeBruijn indices when substituting the self type    into the method signature.

Previously, the DeBruijn index for the self type was not being
adjusted to account for the fn binder. This mean that when late-bound
regions were instantiated, you sometimes wind up with two distinct
lifetimes.

Fixes #19537.
During method resolution, only reborrow if we are not doing an auto-ref.
The current behavior leads to adjustments like `&&*` being applied
instead of just `&` (when the unmodified receiver is a `&T` or an `&mut
T`). This causes both safety errors and unexpected behavior. The safety
errors result from regionck not being prepared for auto-ref-ref-like
adjustments; this is worth fixing on its own, but I think the best way
to do it is to modify regionck to use expr-use-visitor (and fix
expr-use-visitor as well, which I don't think properly invokes `borrow`
for each level of auto-ref), and for now it's simpler to just not
produce the adjustment in question. (I have a separate patch porting
regionck to use exprusevisitor for a different bug, so that is coming.)
auto merge of #19617 : nikomatsakis/rust/issue-19261-2, r=nick29581

**First commit.** Patch up debruijn indices. Fixes #19537. 

**Second commit.** Stop reborrowing so much. Fixes #19147. Fixes #19261.

r? @nick29581