Rollup merge of #87953 - m-ou-se:closure-migration-multiline-formatting, r=petrochenkov

Rollup merge of #87953 - m-ou-se:closure-migration-multiline-formatting, r=petrochenkov

Improve formatting of closure capture migration suggestion for multi-line closures.

Fixes https://github.com/rust-lang/rust/issues/87952

Before:
```
help: add a dummy let to cause `a` to be fully captured
  |
5 ~     let _ = || { let _ = &a;
6 +         dbg!(a.0);
7 ~     };
  |
```

After:
```
help: add a dummy let to cause `a` to be fully captured
  |
5 ~     let _ = || {
6 +         let _ = &a;
7 +         dbg!(a.0);
8 ~     };
  |
```