feat: support Unchained p2wsh path

[Shadouts]

Unchained plans to support p2wsh using the same m/45 path we use for p2sh. This change adds the UNCHAINED_ patterns to bitcoin InputScriptType.SPENDP2SHWITNESS.

[andrewkozlik]

It is best practice to differentiate the BIP 32 path depending on script type, for example m/44'/... for P2PKH and m/84'/... for P2WPKH. As far as I can see, in Trezor firmware the only exception until now has been PATTERN_GREENADDRESS_A and PATTERN_GREENADDRESS_B.

There are two main reasons for this practice, which apply in this case:

• Using different paths with different script types makes account discovery simpler in terms of scanning the blockchain, because the BIP 32 path then fully determines the scriptPubKey and address.
• Reusing the same path with a different script type makes it more easy to commit public key reuse, because the wallet app needs to be aware of all possible script types and scan the blockchain accordingly. Older wallet apps may not be aware of the use of newer script types and may therefore inadvertently reuse public keys when generating new receive addresses or new change-output addresses.

Furthermore, I see that you are using the subtree m / 45' / **, but you use different paths than the one specified in BIP 45, which as far as I can tell is in violation of BIP 43. Now is a good opportunity to fix this issue by defining a distinct path for Unchained's P2WSH scheme.

That being said, I think that none of the above is a strict blocker for merging this PR.

[matejcik]

code change ACK. @Shadouts please add a changelog entry.

[andrewkozlik]

Also squash into a single commit and force-push.

[andrewkozlik]

Note that for your own benefit, it would be wise to add a device test to tests/device_tests/bitcoin/test_nonstandard_paths.py. This is not a requirement, just best practice.

As you are probably aware, this PR does not modify the behavior of Trezor 1 firmware. Again, it's not a requirement from our side, I am only stating this to make sure that it's clear.

[Shadouts]

Changelog added, squashed, and force pushed.