refactor: Reduce number of LoadChainstate parameters and return values

Summary:
and factor out LoadVerifyActivateChainstate()

This is a backport of core#25308
and https://github.com/bitcoin/bitcoin/pull/25667/commits/cced4e7336d93a2dc88e4a61c49941887766bd72

Squashing the backport with the refactoring commit from core#25667 ensures we don't temporarily shadow the other options variable in TestingSetup::TestingSetup

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14614