Auto merge of #46733 - nikomatsakis:nll-master-to-rust-master-5, r=arielb1

nll part 5

Next round of changes from the nll-master branch.

Extensions:

- we now propagate ty-region-outlives constraints out of closures and into their creator when necessary
- we fix a few ICEs that can occur by doing liveness analysis (and the resulting normalization) during type-checking
- we handle the implicit region bound that assumes that each type `T` outlives the fn body
- we handle normalization of inputs/outputs in fn signatures

Not included in this PR (will come next):

- handling `impl Trait`
- tracking causal information
- extended errors

r? @arielb1

src/librustdoc/clean/mod.rs

@@ -1055,6 +1055,7 @@ impl Clean<Option<Lifetime>> for ty::RegionKind {
             ty::ReVar(..) |
             ty::ReSkolemized(..) |
             ty::ReEmpty |
+            ty::ReClosureBound(_) |
             ty::ReErased => None
         }
     }