test: Add BitcoinTestFramework::sync_* methods

Summary:
Partial backport of core PR15773:
https://github.com/bitcoin/bitcoin/pull/15773/commits/fa6dc7c5c3477bda04481f080d430f63539974e2

Depends on D6150 and D6151.

Test Plan:

ninja check-functional

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D6152