Rollup merge of #108834 - compiler-errors:fn-ptr-fn-obl, r=spastorino

Do not ICE when we have fn pointer `Fn` obligations with bound vars in the self type

We never supported solving `for<'a> fn(&'a ()): Fn(&'a ())` -- I tried to add that support in #104929, but iirc `@lcnr` wanted to support this more generally by eagerly instantiating trait predicate binders with placeholders. That never happened due to blockers in the old solver, but we probably shouldn't ICE in any case.

On the bright side, this passes on the new solver :^)

Author: matthiaskrgr