Summary:
## Background
Compaction statistics are collected at various levels across different classes and structs.
* `InternalStats::CompactionStats`: Per-level Compaction Stats within a job (can be at subcompaction level which later get aggregated to the compaction level)
* `InternalStats::CompactionStatsFull`: Contains two per-level compaction stats - `output_level_stats` for primary output level stats and `proximal_level_stats` for proximal level stats. Proximal level statistics are only relevant when using Tiered Storage with the per-key placement feature enabled.
* `InternalStats::CompactionOutputsStats`: Simplified version of `InternalStats::CompactionStats`. Only has a subset of fields from `InternalStats::CompactionStats`
* `CompactionJobStats`: Job-level Compaction Stats. (can be at subcompaction level which later get aggregated to the compaction level)
Please note that some fields in Job-level stats are not in Per-level stats and they don't map 1-to-1 today.
## Issues
* In non-remote compactions, proximal level compaction statistics were not being aggregated into job-level statistics. Job level statistics were missing stats for proximal level for tiered storage compactions with per-key-replacement feature enabled.
* During remote compactions, proximal level compaction statistics were pre-aggregated into job-level statistics on the remote side. However, per-level compaction statistics were not part of the serialized compaction result, so that primary host lost that information and weren't able to populate `per_key_placement_comp_stats_` and `internal_stats_.proximal_level_stats` properly during the installation.
* `TieredCompactionTest` was only checking if (expected stats > 0 && actual stats > 0) instead actual value comparison
## Fixes
* Renamed `compaction_stats_` to `internal_stats_` for `InternalStats::CompactionStatsFull` in `CompactionJob` for better readability
* Removed the usage of `InternalStats::CompactionOutputsStats` and consolidated them to `InternalStats::CompactionStats`.
* Remote Compactions now include the internal stats in the serialized `CompactionServiceResult`. `output_level_stats` and `proximal_level_stats` get later propagated in sub_compact output stats accordingly.
* `CompactionJob::UpdateCompactionJobStats()` now takes `CompactionStatsFull` and aggregates the `proximal_level_stats` as well
* `TieredCompactionTest` is now doing the actual value comparisons for input/output file counts and record counts. Follow up is needed to do the same for the bytes read / written.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13464
Test Plan:
Unit Tests updated to verify stats
```
./compaction_service_test
```
```
./tiered_compaction_test
```
Reviewed By: pdillinger
Differential Revision: D71220393
Pulled By: jaykorean
fbshipit-source-id: ad70bffd9614ced683f90c7570a17def9b5c8f3f
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