db: refactor/cleanup compaction iterator #3082
Description
- Remove the compaction trailer optimization [1]. It's not particularly important in the context of a compaction and we have very subtle invariants involved.
- Explicitly enumerate all key kinds db: extend compaction iterator comments, tests #3081 (review)
- Use the
keyspan.InterleavingIterto interleave range deletions at the maximal sequence number. This will simplify the logic considerably and allow us to eliminate thesameStripeNonSkippablecase.