92b2f5306b test: add dumptxoutset RPC test (James O'Beirne)
c1ccbc3dde devtools: add utxo_snapshot.sh (James O'Beirne)
57cf74c991 rpc: add dumptxoutset (James O'Beirne)
92fafb3a7d coinstats: add coins_count (James O'Beirne)
707fde7b9b add unused SnapshotMetadata class (James O'Beirne)
Pull request description:
This is part of the [assumeutxo project](https://github.com/bitcoin/bitcoin/projects/11):
Parent PR: #15606
Issue: #15605
Specification: https://github.com/jamesob/assumeutxo-docs/tree/master/proposal
---
This changeset defines the serialization format for UTXO snapshots and adds an RPC command for creating them, `dumptxoutset`. It also adds a convenience script for generating and verifying snapshots at a certain height, since that requires doing a hacky rewind of the chain via `invalidateblock`.
All of this is unused at the moment.
ACKs for top commit:
laanwj:
ACK 92b2f5306b
Tree-SHA512: 200dff87767f157d627e99506ec543465d9329860a6cd49363081619c437163a640a46d008faa92b1f44fd403bfc7a7c9e851c658b5a4849efa9a34ca976bf31