Placeholder span used when trait uses a HRTB on itself

[CAD97]

Given the following code: [playground]

pub trait Pack<'a> {
    fn pack()
    where
        Self: for<'x> Pack<'x>;
}

The current output is:

error[E0283]: type annotations needed
  |
  = note: cannot satisfy `Self: Pack<'a>`

This should at least point at the Self: for<'x> Pack<'x> bound.

Ideally, this should work. (It's unclear why it shouldn't, given other where Self: work fine.)

[ChayimFriedman2]

As for the "it should work", see #84435.