Engine: references to const items in traits not imported properly

[paulmure]

Consider this code:

trait Foo {
    const BAR: u64;
}

fn use_foo<T: Foo>() -> u64 {
    T::BAR
}

The reference to T::BAR becomes a GlobalVar pointing to FOO::BAR like this:

[
  "GlobalVar",
  [
    "Concrete",
    {
      "def_id": {
        "krate": "scratch",
        "path": [
          {
            "data": ["TypeNs", "Foo"],
            "disambiguator": 0
          },
          {
            "data": ["ValueNs", "BAR"],
            "disambiguator": 0
          }
        ]
      },
      "kind": ["AssociatedItem", ["Value"]]
    }
  ]
]

However, the reference to the type variable T is not imported.