rustfmt incorrectly fixes parens in template constraints

[medwards]

In the following example rustfmt removes the leading parenthesis in F: (Fn(&T) -> String) but doesn't remove the closing parenthesis (but does add some spacing).

fn make_map<T, F: (Fn(&T) -> String)>(records: &Vec<T>, key_fn: F) -> HashMap<String, usize> {
    records
        .iter()
        .enumerate()
        .map(|(index, record)| (key_fn(record), index))
        .collect()
}

[topecongiro]

The problem here is that the AST node of TyParamBound does not hold information about parenthesis in its field nor span, and rustfmt incorrectly assumes that the closing parenthesis is some kind of comments.