Merge bitcoin/bitcoin#27307: wallet: track mempool conflicts with wallet transactions

5952292133 wallet, rpc: show mempool conflicts in `gettransaction` result (ishaanam)
54e07ee22f wallet: track mempool conflicts (ishaanam)
d64922b590 wallet refactor: use CWalletTx member functions to determine tx state (ishaanam)
ffe5ff1fb6 scripted-diff: wallet: s/TxStateConflicted/TxStateBlockConflicted (ishaanam)
180973a941 test: Add tests for wallet mempool conflicts (ishaanam)

Pull request description:

  The `mempool_conflicts` variable is added to `CWalletTx`, it is a set of txids of txs in the mempool conflicting with the wallet tx or a wallet tx's parent. This PR only changes how mempool-conflicted txs are dealt with in memory.

  `IsSpent` now returns false for an output being spent by a mempool conflicted transaction where it previously returned true.

  A txid is added to `mempool_conflicts` during  `transactionAddedToMempool`. A txid is removed from `mempool_conflicts` during  `transactionRemovedFromMempool`.

  This PR also adds a `mempoolconflicts` field to the `gettransaction` wallet RPC result.

  Builds on #27145
  Second attempt at #18600

ACKs for top commit:
  achow101:
    ACK 5952292133
  ryanofsky:
    Code review ACK 5952292133. Just small suggested changes since last review
  furszy:
    ACK 59522921

Tree-SHA512: 615779606723dbb6c2e302681d8e58ae2052ffee52d721ee0389746ddbbcf4b4c4afacf01ddf42b6405bc6f883520524186a955bf6b628fe9b3ae54cffc56a29

test/functional/wallet_abandonconflict.py

@@ -231,7 +231,11 @@ class AbandonConflictTest(BitcoinTestFramework):
         balance = newbalance
 
         # Invalidate the block with the double spend. B & C's 10 BTC outputs should no longer be available
-        self.nodes[0].invalidateblock(self.nodes[0].getbestblockhash())
+        blk = self.nodes[0].getbestblockhash()
+        # mine 10 blocks so that when the blk is invalidated, the transactions are not
+        # returned to the mempool
+        self.generate(self.nodes[1], 10)
+        self.nodes[0].invalidateblock(blk)
         assert_equal(alice.gettransaction(txAB1)["confirmations"], 0)
         newbalance = alice.getbalance()
         assert_equal(newbalance, balance - Decimal("20"))