[bisect] Print search space with ascii characters

Printing the matrix in a visual way was removed in a recent change. This
adds that back.

Change-Id: If2fe881b44e12208db53312e7c145ebdd9a5a17f
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1561137
Commit-Queue: Jerry Belton <jcecil@google.com>
Reviewed-by: Aidan Wolter <awolter@google.com>