Change rewrite return type from Option to Return

[scampi]

In issues #3206 #3416 #3135, wrap_str is preventing some possibly good formatting because of long strings. The return type being an Option, the fact that the rewrite failed because of a long string is lost.
If that were returning a Return, then the failure reason could be passed up for the callee to handle as appropriate.

For example, it seems the rewrite in #3416 could allow the line to overflow (which anyway would be caught by the LineOverflow logic). However, there are cases where a better formatting is possible, e.g.:

// original
fn foo() {
    let suuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuum = xxxxxxx
        .map(|x| x + 5)
        .map(|x| x / 2)
        .fold(0, |acc, x| acc + x);
}

// formatted
fn foo() {
     let suuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuum =
         xxxxxxx.map(|x| x + 5)
                .map(|x| x / 2)
                .fold(0, |acc, x| acc + x);
}

Although in that example there is no long string, the current wrap_str logic makes that formatting possible.

With a Return as the return type, rewrite methods could be made more flexible to various kinds of errors.
However, that change would require some heavy refactoring I think.

What do you think about such a change ?

[scampi]

• test for Not formatting any part of function #3524