Mempool improvements, branch ID awareness
Whenever the local chain tip is updated, transactions in the mempool which commit to an
unmineable branch ID (for example, just before a network upgrade activates, where the
next block will have a different branch ID) will be removed.
Includes commits cherry-picked from the following upstream PRs:
- bitcoin/bitcoin#6654
- Only the mempool index change.
- bitcoin/bitcoin#6776
- bitcoin/bitcoin#7020
- bitcoin/bitcoin#6915
Part of #2074.
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