Fixup funcAttributes.

Fixup for https://github.com/D-Programming-Language/dmd/pull/3501 which was missing support for `typeof(func)` or `typeof(&property)`.

I will add this support to the documentation as well.

Note that there is one commented-out test. For some reason the `@system` attribute goes missing when using `typeof(func)` with the trait:

```D
struct S
{
    void testSystem() @system { }
}

void main()
{
    // tuple("@system")
    pragma(msg, typeof(S.testSystem));

    // tuple("@system")
    pragma(msg, __traits(getFunctionAttributes, S.testSystem));

    // tuple()
    pragma(msg, __traits(getFunctionAttributes, typeof(S.testSystem)));
}
```