Factors out the group regexes from callstats.py so the two tools can
share them. When --group is specified, the stats are grouped together
using the callstats.py groupings. Also adds --filter (can be supplied
multiple times) to only show certain groups.

Under the hood, this converts the simple arrays and dictionaries to use
classes to simplify the code somewhat.

Change-Id: If6b548e109212adfdf46fa04e7b21638f84a0e26
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1962864Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65429}