There is no wallet derivation path for funding platform addresses

[pauldelucia]

Issue

There is no wallet derivation path for funding platform addresses.

Proposed solution

Platform address funding from Core requires an asset lock. What key should sign this asset lock? It isn't defined in the DIP or anywhere.

For Identity TopUp and Register, we have keys in wallet derivation paths under the Identity feature path and TopUp and Register subfeatures.

DIP 17 defines Platform Address derivation paths under a Platform Address feature. This feature doesn't have subfeatures like the Identity feature. Instead, it has key_class:

• 0 is for receive addresses
• 1 is reserved for wallet internal / change only keys

The proposed solution:

• 2 can be for funding keys

Draft PR here: #3037
And in rust-dashcore: dashpay/rust-dashcore#403