Suggest trait bound on type parameter when it is unconstrained

Given

```
mented on Jan 26, 2015 •
 trait Foo { fn method(&self) {} }

fn call_method<T>(x: &T) {
    x.method()
}
```

suggest constraining `T` with `Foo`.

src/test/ui/issues/issue-39559.stderr

@@ -4,9 +4,11 @@ error[E0599]: no function or associated item named `dim` found for type `D` in t
 LL |     entries: [T; D::dim()],
    |                     ^^^ function or associated item not found in `D`
    |
-   = help: items from traits can only be used if the trait is implemented and in scope
-   = note: the following trait defines an item `dim`, perhaps you need to implement it:
-           candidate #1: `Dim`
+   = help: items from traits can only be used if the type parameter is bounded by the trait
+help: the following trait defines an item `dim`, perhaps you need to restrict type parameter `D` with it:
+   |
+LL | pub struct Vector<T, D: Dim + Dim> {
+   |                      ^^^^^^^^
 
 error: aborting due to previous error