Auto merge of #88719 - estebank:point-at-arg-for-obligation, r=nagisa

Point at argument instead of call for their obligations

When an obligation is introduced by a specific `fn` argument, point at
the argument instead of the `fn` call if the obligation fails to be
fulfilled.

Move the information about pointing at the call argument expression in
an unmet obligation span from the `FulfillmentError` to a new
`ObligationCauseCode`.

When giving an error about an obligation introduced by a function call
that an argument doesn't fulfill, and that argument is a block, add a
span_label pointing at the innermost tail expression.

Current output:

```
error[E0425]: cannot find value `x` in this scope
 --> f10.rs:4:14
  |
4 |         Some(x * 2)
  |              ^ not found in this scope

error[E0277]: expected a `FnOnce<({integer},)>` closure, found `Option<_>`
 --> f10.rs:2:31
  |
2 |       let p = Some(45).and_then({
  |  ______________________--------_^
  | |                      |
  | |                      required by a bound introduced by this call
3 | |         |x| println!("doubling {}", x);
4 | |         Some(x * 2)
  | |         -----------
5 | |     });
  | |_____^ expected an `FnOnce<({integer},)>` closure, found `Option<_>`
  |
  = help: the trait `FnOnce<({integer},)>` is not implemented for `Option<_>`
```

Previous output:

```
error[E0425]: cannot find value `x` in this scope
 --> f10.rs:4:14
  |
4 |         Some(x * 2)
  |              ^ not found in this scope

error[E0277]: expected a `FnOnce<({integer},)>` closure, found `Option<_>`
 --> f10.rs:2:22
  |
2 |     let p = Some(45).and_then({
  |                      ^^^^^^^^ expected an `FnOnce<({integer},)>` closure, found `Option<_>`
  |
  = help: the trait `FnOnce<({integer},)>` is not implemented for `Option<_>`
```

Partially address #27300. Will require rebasing on top of #88546.

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1998,7 +1998,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                                     &obligation,
                                     &traits::SelectionError::Unimplemented,
                                     false,
-                                    false,
                                 );
                             }
                         }