Add Informational BIP: Multilingual mnemonic display and input conventions

[osem23]

This adds an Informational BIP draft, "Multilingual mnemonic display and input conventions."

A display wordlist is a 2048-entry list in a target language, index-parallel to the canonical English BIP-39 wordlist. PBKDF2 runs only on the canonical
English mnemonic; native-language renderings are a display and input layer with no new cryptographic surface; every seed produced under the convention is
restorable in any BIP-39 wallet via its English form.

Reference implementation (MIT): https://github.com/osem23/bip39-wordlists-tzur

It ships 30 index-paired display wordlists with bidirectional mappings, the 10 canonical BIP-39 wordlists preserved byte-for-byte for spec comparison, a
reference validator enforcing every MUST clause, reference decoders in Python, JavaScript, and Swift producing byte-identical seeds, and per-language
conformance test vectors across the five BIP-39 entropy lengths.

Shipped in production by the TZUR Wallet suite (iPhone and Windows).

Per BIP-2, announced on the bitcoindev mailing list (post pending list moderation; archive link to follow).

I have not self-assigned a BIP number. License: BSD-2-Clause (document), MIT (reference implementation).

[jonatack]

@osem23 Thank you for your proposal, but it was opened here prematurely before community discussion of your idea on the mailing list. Please see the README and BIP 3 for the process (thanks!)