Merge #13079: Fix rescanblockchain rpc to properly report progress

Summary:
16be13345 Fix rescanblockchain rpc to property report progress (Ben Woosley)

Pull request description:

Previously it assumed tip in all cases. This also extracts a RescanVerificationProgress helper object whose role is to manage reporting, in order to simplify ScanForWalletTransactions - more lines in total, but much simpler to follow the core logic.

Tree-SHA512: 5ebed0c56fae4ccfe613ff1d7082cb6da5a86635a8993ed3af70b500a4ea43074121aea9219b2f0321fbfeb7efcb964bdc2199297a64ca0fa85d9d07aa637d40

Backport of Core PR13079
https://github.com/bitcoin/bitcoin/pull/13079/

Test Plan:

make check
./bitcoind --printtoconsole
./bitcoin-cli rescanblockchain 0 1300000

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

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

Differential Revision: https://reviews.bitcoinabc.org/D4112