[BIP] Normalized transaction IDs

Christian Decker, a member of the bitcoin-dev community, suggests that normalized transaction IDs can help in certain scenarios. Specifically, they are useful when a single signer wants to follow up on a transaction with another transaction that spends the first one's change output. In addition, these IDs prevent any modification in a multi-signer scenario. However, for ordinary transactions that do not involve smart contracts, canonical encoding is a better option as it is readily available and does not come with associated costs such as new pubkey type adoption, UTXO size increase, or the need for nodes to fix txid references. Decker also cautions against overselling the importance of this approach, emphasizing that while it is good and important to work on, it should not be overstated.