Function rustfmt_nightly::items::rewrite_where_keyword

fn rewrite_where_keyword(
    context: &RewriteContext<'_>,
    predicates: &[WherePredicate],
    where_span: Span,
    shape: Shape,
    span_end_before_where: BytePos,
    where_clause_option: WhereClauseOption
) -> Option<(String, bool)>

Rewrite where and comment around it.