Use structured suggestion when telling user about `for<'a>`

```
error[E0637]: `&` without an explicit lifetime name cannot be used here
  --> $DIR/E0637.rs:13:13
   |
LL |     T: Into<&u32>,
   |             ^ explicit lifetime name needed here
   |
help: consider introducing a higher-ranked lifetime here
   |
LL |     T: for<'a> Into<&'a u32>,
   |        +++++++       ++
```

1 files changed, 7 insertions, 3 deletions

diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 9f4573ea025..744dcf0db84 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -1632,9 +1632,13 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                                 ..
                             } = &rib.kind
                             {
-                                diag.span_help(
-                                    *span,
-                                    "consider introducing a higher-ranked lifetime here with `for<'a>`",
+                                diag.multipart_suggestion(
+                                    "consider introducing a higher-ranked lifetime here",
+                                    vec![
+                                        (span.shrink_to_lo(), "for<'a> ".into()),
+                                        (lifetime.ident.span.shrink_to_hi(), "'a ".into()),
+                                    ],
+                                    Applicability::MachineApplicable,
                                 );
                                 break;
                             }