no auto-completion for associated constants/functions on primitive types

[japaric]

the auto-completion list for this case with a primitive type is empty:

let x = i16::_;

the auto-completion list for this other case with a user-defined type does list the associated constants and functions:

struct S;
impl S {
    const A: u8 = 0;
    const B: u8 = 0;
    fn foo() {}
}
let x = S::_; // [A, B, foo]

[jonas-schievink]

We don't complete functions either