[Part 5 of 5] Add a CChainState class to clarify internal interfaces
Summary:
Move some additional variables into CChainState private
Backport of Core PR 10279 commit 2862aca
https://github.com/bitcoin/bitcoin/pull/10279/commits/2862aca40f24acc48d3052d5ba3f639e3fc0a621
Depends on D1971 and D2645
T572
Test Plan:
make check test_runner.py --extended
Reviewers: #bitcoin_abc, schancel, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Subscribers: markblundeberg, teamcity
Differential Revision: https://reviews.bitcoinabc.org/D1972