Allows dapps to cache the raw PathXpub[] from wallet_ready and restore
them on subsequent page loads. restoreSessionPaths decodes the xpub strings
and populates pubkeyState so getPubkey() works without waiting for the
wallet to reconnect. Throws on invalid xpub data.
This solves an issue where wallet has to scan address ranges for each
derivation path and match it to locking script to figure out what
private key to use for signature.
This is a waste of effort and unnecessary complex for wallet
implementations since the dapp side already knows what inputs its using.
