This CL updates argument parsing mechanism from using a custom implementation + optparse to argparse. It is intended to clear tech debt for future changes.

Change-Id: I06ba5d3c532638a7970be960e02ebbafbea9dcb0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3541479Reviewed-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>