Implement method to find reports by type

[mkatychev]

Report should havea a filter/find method to get all reports of a given type.

fn iter_downcast_reports<T: 'static>(
    report: &Report<impl ?Sized, Mutable, Local>,
) -> impl Iterator<Item = &T> {
    report
        .iter_reports()
        .filter_map(|r| r.downcast_current_context::<T>())
}

prior art:

• error_stack::Report::downcast_ref
• std::iter::Iterator::findk