This is important for multiple compaction groups, as they cannot share state that must span a single SSTable set.
The solution is about:
1) Decoupling compaction strategy from its state; making compaction_strategy a pure stateless entity
2) Each compaction group storing its own compaction strategy state
3) Compaction group feeds its state into compaction strategy whenever needed
Closes#13351
* github.com:scylladb/scylladb:
compaction: TWCS: wire up compaction_strategy_state
compaction: LCS: wire up compaction_strategy_state
compaction: Expose compaction_strategy_state through table_state
replica: Add compaction_strategy_state to compaction group
compaction: Introduce compaction_strategy_state
compaction: add table_state param to compaction_strategy::notify_completion()
compaction: LCS: extract state into a separate struct
compaction: TWCS: prepare for stateless strategy
compaction: TWCS: extract state into a separate struct
compaction: add const-qualifier to a few compaction_strategy methods
472b155d76