Expose xpub in ExtendeKeyInfo

[allisonmoyer]

Related to issue #138 and pull request #139 - our team wants the ability to use xpubs in wallet descriptors when creating a wallet and later sign transactions with the xprv, so we need a reference to the xpub in the ExtendedKeyInfo

cc @notmandatory

[notmandatory]

Do you need to also sign arbitrary messages as in #139? Or just be able to make a watch only descriptor with xpubs and also sign PSBTs with an xprv based version of the same descriptor? If the later I think #154 will provide what you need.

[allisonmoyer]

Ah, I didn't see #154, yeah that's exactly what we're looking for at this point, thanks. Any rough idea of timeline for #154 completion?

[notmandatory]

We just merged @dhruv-1001's PR #154 which should do what you want. It will be in the next releases of bdk-ffi, bdk-kotlin, and bdk-swift.