This commit adds a new callback `MempoolTransactionsRemovedForBlock` which notify
its listeners of the transactions that are removed from the mempool because a new
block is connected, along with the block height the transactions were removed.
The transactions are in `RemovedMempoolTransactionInfo` format.
`CTransactionRef`, base fee, virtual size, and height which the transaction was added
to the mempool are all members of the struct called `RemovedMempoolTransactionInfo`.
A struct `NewMempoolTransactionInfo`, which has fields similar to `RemovedMempoolTransactionInfo`,
will be added in a later commit, create a struct `TransactionInfo` with all similar fields.
They can both have a member with type `TransactionInfo`.
Allows calling UpdateLockPoints() with a (const) txiter. Note that this
was already possible for caller using mapTx.modify(txiter). The point
here is to not be accessing mapTx when doing so.
This is a refactor as long as no signed integer overflow appears. In
normal operation and absent bugs, signed integer overflow should never
happen in the touched code paths.
The main benefit of this refactor is to drop the file-wide ubsan
suppression unsigned-integer-overflow:txmempool.cpp.
For now, this only changes the internal private representation and the
publicly returned type remains uint64_t.
