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>,
   |        +++++++       ++
```

Author: estebank

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;
                             }

tests/ui/error-codes/E0637.stderr

@@ -22,11 +22,10 @@ error[E0637]: `&` without an explicit lifetime name cannot be used here
 LL |     T: Into<&u32>,
    |             ^ explicit lifetime name needed here
    |
-help: consider introducing a higher-ranked lifetime here with `for<'a>`
-  --> $DIR/E0637.rs:13:8
+help: consider introducing a higher-ranked lifetime here
    |
-LL |     T: Into<&u32>,
-   |        ^
+LL |     T: for<'a> Into<&'a u32>,
+   |        +++++++       ++
 
 error: aborting due to 3 previous errors
 

tests/ui/generics/issue-65285-incorrect-explicit-lifetime-name-needed.stderr

@@ -4,11 +4,10 @@ error[E0637]: `&` without an explicit lifetime name cannot be used here
 LL | fn should_error<T>() where T : Into<&u32> {}
    |                                     ^ explicit lifetime name needed here
    |
-help: consider introducing a higher-ranked lifetime here with `for<'a>`
-  --> $DIR/issue-65285-incorrect-explicit-lifetime-name-needed.rs:5:32
+help: consider introducing a higher-ranked lifetime here
    |
-LL | fn should_error<T>() where T : Into<&u32> {}
-   |                                ^
+LL | fn should_error<T>() where T : for<'a> Into<&'a u32> {}
+   |                                +++++++       ++
 
 error[E0106]: missing lifetime specifier
   --> $DIR/issue-65285-incorrect-explicit-lifetime-name-needed.rs:9:20

tests/ui/underscore-lifetime/where-clause-inherent-impl-ampersand-rust2015.fixed

@@ -0,0 +1,17 @@
+// run-rustfix
+
+trait WithType<T> {}
+trait WithRegion<'a> { }
+
+#[allow(dead_code)]
+struct Foo<T> {
+    t: T
+}
+
+impl<T> Foo<T>
+where
+    T: for<'a> WithType<&'a u32>
+//~^ ERROR `&` without an explicit lifetime name cannot be used here
+{ }
+
+fn main() {}

tests/ui/underscore-lifetime/where-clause-inherent-impl-ampersand-rust2015.rs

@@ -0,0 +1,17 @@
+// run-rustfix
+
+trait WithType<T> {}
+trait WithRegion<'a> { }
+
+#[allow(dead_code)]
+struct Foo<T> {
+    t: T
+}
+
+impl<T> Foo<T>
+where
+    T: WithType<&u32>
+//~^ ERROR `&` without an explicit lifetime name cannot be used here
+{ }
+
+fn main() {}

tests/ui/underscore-lifetime/where-clause-trait-impl-region.rust2015.stderr renamed to tests/ui/underscore-lifetime/where-clause-inherent-impl-ampersand-rust2015.stderr

@@ -1,14 +1,13 @@
 error[E0637]: `&` without an explicit lifetime name cannot be used here
-  --> $DIR/where-clause-trait-impl-region.rs:11:17
+  --> $DIR/where-clause-inherent-impl-ampersand-rust2015.rs:13:17
    |
 LL |     T: WithType<&u32>
    |                 ^ explicit lifetime name needed here
    |
-help: consider introducing a higher-ranked lifetime here with `for<'a>`
-  --> $DIR/where-clause-trait-impl-region.rs:11:8
+help: consider introducing a higher-ranked lifetime here
    |
-LL |     T: WithType<&u32>
-   |        ^
+LL |     T: for<'a> WithType<&'a u32>
+   |        +++++++           ++
 
 error: aborting due to previous error
 

tests/ui/underscore-lifetime/where-clause-inherent-impl-ampersand-rust2018.fixed

@@ -0,0 +1,18 @@
+// edition:2018
+// run-rustfix
+
+trait WithType<T> {}
+trait WithRegion<'a> { }
+
+#[allow(dead_code)]
+struct Foo<T> {
+    t: T
+}
+
+impl<T> Foo<T>
+where
+    T: for<'a> WithType<&'a u32>
+//~^ ERROR `&` without an explicit lifetime name cannot be used here
+{ }
+
+fn main() {}

tests/ui/underscore-lifetime/where-clause-inherent-impl-ampersand-rust2018.rs

@@ -0,0 +1,18 @@
+// edition:2018
+// run-rustfix
+
+trait WithType<T> {}
+trait WithRegion<'a> { }
+
+#[allow(dead_code)]
+struct Foo<T> {
+    t: T
+}
+
+impl<T> Foo<T>
+where
+    T: WithType<&u32>
+//~^ ERROR `&` without an explicit lifetime name cannot be used here
+{ }
+
+fn main() {}

tests/ui/underscore-lifetime/where-clause-trait-impl-region.rust2018.stderr renamed to tests/ui/underscore-lifetime/where-clause-inherent-impl-ampersand-rust2018.stderr

@@ -1,14 +1,13 @@
 error[E0637]: `&` without an explicit lifetime name cannot be used here
-  --> $DIR/where-clause-trait-impl-region.rs:11:17
+  --> $DIR/where-clause-inherent-impl-ampersand-rust2018.rs:14:17
    |
 LL |     T: WithType<&u32>
    |                 ^ explicit lifetime name needed here
    |
-help: consider introducing a higher-ranked lifetime here with `for<'a>`
-  --> $DIR/where-clause-trait-impl-region.rs:11:8
+help: consider introducing a higher-ranked lifetime here
    |
-LL |     T: WithType<&u32>
-   |        ^
+LL |     T: for<'a> WithType<&'a u32>
+   |        +++++++           ++
 
 error: aborting due to previous error