Point at bound introducing obligation of call parameter for where clause bounds

[estebank]

The following code

rust/src/test/ui/where-clauses/where-clauses-method-unsatisfied.rs

Lines 10 to 20 in 38e5764

	impl<T> Foo<T> {
	fn equals(&self, u: &Foo<T>) -> bool where T : Eq {
	self.value == u.value
	}
	}
	fn main() {
	let x = Foo { value: Bar };
	x.equals(&x);
	//~^ ERROR `Bar: Eq` is not satisfied
	}

emits

rust/src/test/ui/where-clauses/where-clauses-method-unsatisfied.stderr

Lines 1 to 9 in 38e5764

	error[E0277]: the trait bound `Bar: Eq` is not satisfied
	--> $DIR/where-clauses-method-unsatisfied.rs:18:14
	|
	LL | x.equals(&x);
	| ------ ^^ the trait `Eq` is not implemented for `Bar`
	| |
	| required by a bound introduced by this call
	error: aborting due to previous error

It should point at the where T : Eq bound as well.

Noticed in https://github.com/rust-lang/rust/pull/88719/files#r708156543:

This case has a MiscObligation, so for some where clauses we need to do better, but at least we point at the relevant argument. The new span pointing at the call at least hints at the user that they should look at the equals implementation to figure out why the bound was added.

[compiler-errors]

Was this fixed by #89580?

[compiler-errors]

For the record, we now error with:

error[[E0277]](https://doc.rust-lang.org/stable/error-index.html#E0277): the trait bound `Bar: Eq` is not satisfied
  --> src/main.rs:13:15
   |
13 |      x.equals(&x); 
   |        ------ ^^ the trait `Eq` is not implemented for `Bar`
   |        |
   |        required by a bound introduced by this call
   |
note: required by a bound in `Foo::<T>::equals`
  --> src/main.rs:6:53
   |
6  |      fn equals(&self, u: &Foo<T>) -> bool where T : Eq { 
   |                                                     ^^ required by this bound in `Foo::<T>::equals`
help: consider annotating `Bar` with `#[derive(Eq)]`
   |
1  | #[derive(Eq)]
   |

Note the "note"

[estebank]

Yeah, that seems good to me.