Provide associated type information in method chains

When encountering an unmet obligation that affects a method chain, like
in iterator chains where one of the links has the wrong associated
type, we point at every method call and mention their evaluated
associated type at that point to give context to the user of where
expectations diverged from the code as written.

```
note: the expression is of type `Map<std::slice::Iter<'_, {integer}>, [closure@$DIR/invalid-iterator-chain.rs:12:18: 12:21]>`
  --> $DIR/invalid-iterator-chain.rs:12:14
   |
LL |         vec![0, 1]
   |         ---------- this expression has type `Vec<{integer}>`
LL |             .iter()
   |              ------ associated type `std::iter::Iterator::Item` is `&{integer}` here
LL |             .map(|x| { x; })
   |              ^^^^^^^^^^^^^^^ associated type `std::iter::Iterator::Item` is `()` here
```

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