Support Slip-132 variants

[nk1tz]

Add SLIP-132 extended public key support (zpub, ypub, vpub, upub)

Hey @landabaso, I know this might sound crazy, but I keep coming across applications that are constructing descriptors with slip-132 variants even though the concept of the descriptor itself renders this a redundant expression of intent...

Here is a solution to transmute encountered variants to the standard x|t versions that bip32 expects.
Of course I could pre-transform descriptors prior to passing them to this library, but I wanted to see what you thought of this idea.

Changes

• Updated regex in re.ts to accept zpub/ypub/vpub/upub prefixes (and their uppercase multisig variants)
• Added convertToStandardXpub() in keyExpressions.ts that converts SLIP-132 keys to xpub/tpub by swapping version bytes before passing to bip32
• Added test vectors proving zpub/ypub/vpub/upub descriptors derive the same addresses as their xpub/tpub equivalents

[landabaso]

Thanks for the detailed writeup. I agree it's not crazy, I've seen apps do that too.

I'm going to close this though. I want this library to stay strict and not carry legacy SLIP-132 (ypub/zpub…) compatibility... If an app is still embedding SLIP-132 into descriptors, I'd rather push it to move forward and normalize to xpub/tpub.

Funny detail: bitcoinerlab had SLIP-132 support early on and I removed it years ago for exactly this reason:
https://github.com/bitcoinerlab/farvault-lib/blob/41dfcd90d07e078f0eaf551a48a60375a899990b/src/bip44/index.js#L81

Thanks again for the contribution and sorry for turning this down (again, I know!) :-(