Add unit tests for signals generated by ProcessNewBlock()

Summary:
After a recent bug discovered in callback ordering in MainSignals,
this test checks invariants in ordering of
BlockConnected / BlockDisconnected / UpdatedChainTip signals

This is a partial backport of Core PR13023 : https://github.com/bitcoin/bitcoin/pull/13023/commits/dd435ad40267f5c50ff17533c696f9302829a6a6

Depends on D3436

Test Plan:

make check

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D3437