[feature]: unify address creation behavior between BtcWalletKeyRing.DeriveNextKey and BtcWalletKeyRing.DeriveKey

[jharveyb]

Is your feature request related to a problem? Please describe.

Discovered during tapd work and documented further here: lightninglabs/taproot-assets#883

The DeriveNextKey method stores a P2WKH address associated with the generated key:

lnd/keychain/btcwallet.go

Line 164 in 675ae6e

addrs, err := scope.NextExternalAddresses(

Which is used elsewhere to look up KeyLocator info for a given pubkey when signing:

lnd/lnwallet/rpcwallet/rpcwallet.go

Line 973 in 675ae6e

managedAddr, err := r.AddressInfo(addr)

DeriveKey does not store an address associate with a derived key:

lnd/keychain/btcwallet.go

Line 230 in 675ae6e

path := waddrmgr.DerivationPath{

So such keys are omitted from RPC output like ListAccounts or ListAddresses. This means that RPC users cannot recover the KeyLocator for a key derived with DeriveKey (and the node itself will fail this recovery, so trying to sign with such a key will fail.)

Describe the solution you'd like

Update to DeriveKey that stores a matching P2WKH address, so these RPC calls have matching behavior.

Describe alternatives you've considered

Repeatedly calling DeriveNextKey until I get to the desired index, which seems strictly worse.