Replace Lister With Function Using Iterators

[krakow10]

Not the most important part of rbx-dom, but hey it's -38 loc. The only functional difference should be that the faces are printed in all caps. Updating bitflags shouldn't be a breaking change because it's a private type in a private field.

Here's a small test that I ran to prove it works:

#[test]
fn single() {
    let f = Faces {
        flags: FaceFlags::BACK,
    };
    let text = format!("{f:?}");
    assert_eq!(text, "Faces(BACK)");
}
#[test]
fn double() {
    let f = Faces {
        flags: FaceFlags::BOTTOM | FaceFlags::RIGHT,
    };
    let text = format!("{f:?}");
    assert_eq!(text, "Faces(RIGHT, BOTTOM)");
}

[Dekkonot]

I'm not actually convinced this provides any value. Technically it improves Lister... but as you said, that's used for what, the Debug implementation for Faces and Axes?

It doesn't provide enough to warrant changing the debug output for Faces IMO, but I'll invite @kennethloeffler to share his thoughts.