As discussed in #3900 (comment), it'd be preferable in my view to remove the "special case" code for BindingPattern from GetSpan codegen.

I propose instead adding a #[span] attr to the kind field, and codegen can act on that to generate:

impl<'a> GetSpan for BindingPattern<'a> {
    #[inline]
    fn span(&self) -> Span {
        self.kind.span()
    }
}

We can then use that same #[span] mechanism if it's required for any other types in future.