For recursive impl trait point at statement that causes the recursion

[estebank]

After #56074, the error is already good enough:

error[E0720]: opaque type expands to a recursive type
  --> $DIR/recursive-impl-trait-type.rs:6:22
   |
LL | fn option(i: i32) -> impl Sized { //~ ERROR
   |                      ^^^^^^^^^^ expands to self-referential type
   |
   = note: expanded type is `std::option::Option<(impl Sized, i32)>`

but it'd be nice if we pointed at the exact statement causing the recursion:

error[E0720]: opaque type expands to a recursive type
  --> $DIR/recursive-impl-trait-type.rs:6:22
   |
LL | fn option(i: i32) -> impl Sized { //~ ERROR
   |                      ^^^^^^^^^^ expands to self-referential type
...
LL |         Some((option(i - 1), i))
   |         ^^^^^^^^^^^^^^^^^^^^^^^^ expanded type is `std::option::Option<(impl Sized, i32)>`
LL |     }
LL | }

[estebank]

Fixed.