This prepares the addition of `FORCE_SYNC`.
`empty_cache` in `FlushStateToDisk` was moved up to be reusable and `FlushStateMode::FORCE_FLUSH` was used as a placeholder before we properly split the two new states.
`log_utxocache_flush.py` was regenerated and the alignment adjusted for the wider `FlushStateMode` values.
Co-authored-by: Pieter Wuille <pieter@wuille.net>
Co-authored-by: optout <13562139+optout21@users.noreply.github.com>
Change ChainstateRole parameter passed to wallets and indexes. Wallets and
indexes need to know whether chainstate is historical and whether it is fully
validated. They should not be aware of the assumeutxo snapshot validation
process.