Function difft::display::side_by_side::visible_content_max_display_width

fn visible_content_max_display_width(
    lhs_src: &str,
    rhs_src: &str,
    hunks: &[Hunk],
    num_context_lines: u32,
    tab_width: usize
) -> (usize, usize)

Find the longest line in lhs_src and rhs_src that will be displayed. Return the length of that line for both LHS and RHS.