Summary:
Adds compaction statistics (total bytes read and written) for compactions that occur for delete-triggered, periodic, and TTL compaction reasons.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7165

Test Plan:
TTL and periodic can be checked by runnning db_bench with the options activated:

/db_bench --benchmarks="fillrandom,stats" --statistics --num=10000000 -base_background_compactions=16 -periodic_compaction_seconds=1
./db_bench --benchmarks="fillrandom,stats" --statistics --num=10000000 -base_background_compactions=16 -fifo_compaction_ttl=1

Setting the time to one second causes non-zero bytes read/written for those compaction reasons. Disabling them or setting them to times longer than the test run length causes the stats to return to zero as expected.

Delete-triggered compaction counting is tested in DBTablePropertiesTest.DeletionTriggeredCompactionMarking

Reviewed By: ajkr

Differential Revision: D22693050

Pulled By: akabcenell

fbshipit-source-id: d15cef4d94576f703015c8942d5f0d492f69401d