Use multispan suggestions more often

* Use more accurate span for `async move` suggestion
* Use more accurate span for deref suggestion
* Use `multipart_suggestion` more often

Author: estebank

tests/ui/crashes/ice-6250.stderr

@@ -25,10 +25,12 @@ error[E0308]: mismatched types
   --> $DIR/ice-6250.rs:12:14
    |
 LL |         Some(reference) = cache.data.get(key) {
-   |              ^^^^^^^^^
-   |              |
-   |              expected integer, found `&i32`
-   |              help: consider dereferencing the borrow: `*reference`
+   |              ^^^^^^^^^ expected integer, found `&i32`
+   |
+help: consider dereferencing the borrow
+   |
+LL |         Some(*reference) = cache.data.get(key) {
+   |              ^
 
 error[E0308]: mismatched types
   --> $DIR/ice-6250.rs:12:9