pub fn inline_get_field(expr: &mut Expr) {
    expr.transform(&mut |ref mut expr| {
        if let GetField { ref expr, index } = expr.kind {
            if let MakeStruct { ref elems } = expr.kind {
                return Some(elems[index as usize].clone());
            }
        }
        None
    });
}
Inlines GetField(MakeStruct(*)) expressions, which can occur during loop fusion when some
of the loops are zipping together multiple column vectors.
weld/src/optimizer/transforms/inliner.rs