Add scantxoutset RPC method

Summary:

• Add FindScriptPubKey() to search the UTXO set
• Blockchain/RPC: Add scantxoutset method to scan UTXO set
• scantxoutset: add support for scripts
• scantxoutset: support legacy P2PK script type
• [QA] Add scantxoutset test
• scantxoutset: mention that scanning by address will miss P2PK txouts

This is a backport fo Core PR12196

Test Plan:

make check
./test/functional/test_runner.py

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4357