[zlib_bench] Allow user to print results in CSV format

This adds a new option (i.e. --cvs) that will print the results
of a benchmark in a tab separated format.

Usage: ./zlib_bench gzip --cvs ~/corpus/* > zlib_perf.csv

Makes it easier to import the results of a bench run into Google
Sheets (no more typing).

Bug: 798943
Change-Id: I1c0b7d44520a4f721bc6a79d15f0066af2c662ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4668307
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1169709}