[moveonly] Extract HelpRequested to dry up the help options testing

Summary:
This ensures consistency across interfaces and makes the version handling more clear.

Backport of core PR12846

Test Plan: Run help on programs

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2197