Bech32m format for v1+ witness addresses.

Defines Bech32m, a fixed version of the error check used in newer bc1 addresses, including Taproot ones.

The original bc1 address format had a flaw: extra or missing letter 'q's just before a final 'p' could slip past its error check. Bech32m fixes this for newer segwit address versions, such as Taproot's, so wallets can catch that kind of typing mistake. The first segwit addresses keep the original format.