Merge bitcoin/bitcoin#22253: validation: distinguish between same tx and same-nonwitness-data tx in mempool

b7a8cd9963e810264d3b45d0ad15af863965c47a [test] submit same txid different wtxid as mempool tx (glozow)
fdb48163bfbf34f79dc78ffaa2bbf9e39af96687 [validation] distinguish same txid different wtxid in mempool (glozow)

Pull request description:

  On master, if you submit a transaction with the same txid but different witness to the mempool, it thinks the transactions are the same. Users submitting through `BroadcastTransaction()` (i.e. `sendrawtransaction` or the wallet) don't get notified that there's a different transaction in the mempool, although it doesn't crash. Users submitting through `testmempoolaccept()` will get a "txn-already-in-mempool" error.

  This PR simply distinguishes between `txn-already-in-mempool` and `txn-same-nonwitness-data-in-mempool`, without handling them differently: `sendrawtransaction` still will not throw, but `testmempoolaccept` will give you a different error.

  I believe the intention of #19645 is to allow full swaps of transactions that have different witnesses but identical nonwitness data. Returning a different error message + adding a test was suggested: https://github.com/bitcoin/bitcoin/pull/19645#issuecomment-705109193 so this is that PR.

ACKs for top commit:
  naumenkogs:
    ACK b7a8cd9963e810264d3b45d0ad15af863965c47a
  jnewbery:
    Code review ACK b7a8cd9963e810264d3b45d0ad15af863965c47a
  theStack:
    Code-review ACK b7a8cd9963e810264d3b45d0ad15af863965c47a
  darosior:
    re-utACK b7a8cd9963e810264d3b45d0ad15af863965c47a

Tree-SHA512: 9c6591edaf8727ba5b4675977adb8cbdef7288584003b6cd659828032dc92d2ae915800a8ef8b6fdffe112c1b660df72297a3dcf2e2e3e1f959c6cb3678c63ee

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