[Part 4 of 5] Add a CChainState class to clarify internal interfaces

Summary:
Create initial CChainState to hold chain state information

Backport of Core PR 10279 Commit fd4d80a

Depends on D1970
T572

Test Plan:

make VERBOSE=1 check && ./test/functional/test_runner.py

Reviewers: #bitcoin_abc, O1 Bitcoin ABC, jasonbcox, deadalnix

Reviewed By: #bitcoin_abc, O1 Bitcoin ABC, jasonbcox, deadalnix

Subscribers: deadalnix, jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1971