Improve error message for "return type cannot contain a projection or Self..."

[gliderkite]

Following the improvement for the diagnostic of the error reported in this issue #69276, it would be nice (depending on how #61949 is prioritized) to have the same error message when instead of returning Self the function returns Result<Self, Error>.

When Self is returned I get a nice error message (on rustc 1.47):

struct S<'a>(&'a i32);

impl<'a> S<'a> {
    async fn new(i: &'a i32) -> Self {
        S(&22)
    }
}

error[E0760]: `async fn` return type cannot contain a projection or `Self` that references lifetimes from a parent scope
 --> src/lib.rs:4:33
  |
4 |     async fn new(i: &'a i32) -> Self {
  |                                 ^^^^ help: consider spelling out the type instead: `S<'a>`

But if Result<Self, Error> is used I get:

struct S<'a>(&'a i32);

impl<'a> S<'a> {
    async fn new(i: &'a i32) -> Result<Self, ()> {
        Ok(S(&22))
    }
}

error[E0760]: `async fn` return type cannot contain a projection or `Self` that references lifetimes from a parent scope
 --> src/lib.rs:4:33
  |
4 |     async fn new(i: &'a i32) -> Result<Self, ()> {
  |                                 ^^^^^^^^^^^^^^^^

with no suggestion to spell the type.

Link to Playground

[tmandry]

@rustbot remove-assignment

@csmoe feel free to re-claim if you are working on this.