test: Add generatetodescriptor RPC
Summary:
The existing generatetoaddress RPC can only generate to scriptPubKeys that can be represented by an address. However, raw scripts (such as OP_TRUE) or P2PK can not be represented by an address, which complicates testing.
Backport of core PR16943.
Depends on D7983.
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D7984