improve formatting of boolean expression with groups

I think the formatting of the following boolean expression could be improved so that it is clear that:

• the first two operands are OR'ed
• and its result is AND'ed with the third operand.

https://github.com/rust-lang-nursery/rustfmt/blob/075aa909cd2bcdc603f45e0b65119c6a7e3b2030/src/expr.rs#L886-L888

A possible formatting would be:

let force_newline_brace =
    (pat_expr_string.contains('\n') || pat_expr_string.len() > one_line_budget) 
        && !last_line_extendable(&pat_expr_string);

If there is not enough space, we could have something like:

let force_newline_brace =
    (pat_expr_string12345678.contains('\n')
     || pat_expr_string123456789.len() > one_line_budget) 
        && !last_line_extendable(&pat_expr_string);

Start with src/expr.rs around lines 886-888, where the boolean expression is formatted. Compare the current output with the grouped examples in the issue and trace the surrounding formatting logic. Done means rustfmt produces grouping that makes the OR operands and their AND relationship clear, including when the expression wraps.