Intra-L0 compaction reduces usage of trivial move during loads in key order

Prior to intra-L0 compaction when db_bench --benchmarks=fillseq is run with leveled compaction there was no compaction, only trivial moves. I can reproduce that using RocksDB versions 4.1 or 5.1.4. But in v6 once there are a few stalls then some intra-L0 compaction occurs and at that point some compaction is used in place of trivial move. This is related to [issue 9423](https://github.com/facebook/rocksdb/issues/9423) and possibly to issue [10082](https://github.com/facebook/rocksdb/issues/10082).

While the analysis above is based on correlation rather than causation. I also ran tests using version 6.28.2 as-is and then hacked where the hack does: disables intra-L0 compaction, disables dynamic resizing of per-level targets. Then I ran fillseq and the as-is binary gets some trivial move and some compaction while the hacked version only has trivial moves.

Other things that I see:
* write-amp is ~2X larger for the as-is binary because trivial move isn't always used. See the _Cumulative compaction_ line below where it is 1585.01 for as-is versus 878.32 for hacked.
* compaction wall clock seconds is ~3X larger for the as-is binary. From the _Comp(sec)_ column is is 15517.21 vs 4807.7
* there are more write stalls for the hacked binary. I am curious if that can be fixed. The cause was always too many L0 files (147247 level0_slowdown, 107452 level0_slowdown_with_compaction) and 2/3 of those occur when L1->L2 is in progress. Given that Ln->Ln+1 should be fast for trivial move I don't understand why this happens.
* throughput was worse for the hacked binary, but efficiency (see bullet points above) was better. I wonder if the additional stalls from too many L0 files (32.4% vs 22.3%) was the root cause.

A command line is:
```
./db_bench --benchmarks=fillseq --allow_concurrent_memtable_write=false --level0_file_num_compaction_trigger=4 --level0_slowdown_writes_trigger=20 --level0_stop_writes_trigger=30 --max_background_jobs=16 --max_write_buffer_number=8 --db=/data/m/rx --wal_dir=/data/m/rx --num=4000000000 --num_levels=8 --key_size=20 --value_size=400 --block_size=8192 --cache_size=225485783040 --cache_numshardbits=6 --compression_max_dict_bytes=0 --compression_ratio=0.5 --compression_type=lz4 --bytes_per_sync=8388608 --cache_index_and_filter_blocks=1 --cache_high_pri_pool_ratio=0.5 --benchmark_write_rate_limit=0 --write_buffer_size=16777216 --target_file_size_base=16777216 --max_bytes_for_level_base=67108864 --verify_checksum=1 --delete_obsolete_files_period_micros=62914560 --max_bytes_for_level_multiplier=8 --statistics=0 --stats_per_interval=1 --stats_interval_seconds=20 --report_interval_seconds=5 --histogram=1 --memtablerep=skip_list --bloom_bits=10 --open_files=-1 --subcompactions=1 --compaction_style=0 --min_level_to_compress=3 --level_compaction_dynamic_level_bytes=true --pin_l0_filter_and_index_blocks_in_cache=1 --min_level_to_compress=0 --use_existing_db=0 --sync=0 --threads=1 --memtablerep=vector --allow_concurrent_memtable_write=false --disable_wal=1 --seed=1653095086 --report_file=bm.lc.nt32.cm1.d0/v6.28.2.base/benchmark_fillseq.wal_disabled.v400.log.r.csv
```

Compaction IO stats from test end for the as-is binary show that some compaction is used:
```
Level Files Size Score Read(GB) Rn(GB) Rnp1(GB) Write(GB) Wnew(GB) Moved(GB) W-Amp Rd(MB/s) Wr(MB/s) Comp(sec) CompMergeCPU(sec) Comp(cnt) Avg(sec) KeyIn KeyDrop Rblob(GB) Wblob(GB)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
L0 19/4 396.26 MB 4.2 490.6 0.0 490.6 1368.9 878.3 0.0 1.6 37.0 103.4 13561.13 12779.04 115741 0.117 2233M 0 0.0 0.0
L2 58/0 1.20 GB 3.1 216.5 114.0 102.5 214.2 111.7 461.2 1.9 114.4 113.1 1938.53 1928.58 1847 1.050 986M 0 0.0 0.0
L3 65/0 1.41 GB 0.8 1.0 0.7 0.3 1.0 0.7 837.1 1.5 114.6 114.7 9.36 9.32 14 0.669 4773K 0 0.0 0.0
L4 131/0 2.34 GB 0.3 0.6 0.6 0.0 0.6 0.6 867.8 1.0 114.2 114.2 5.47 5.43 26 0.211 2785K 0 0.0 0.0
L5 785/0 12.46 GB 0.3 0.2 0.2 0.0 0.2 0.2 869.8 1.0 112.9 112.9 2.20 2.18 16 0.137 1107K 0 0.0 0.0
L6 6117/0 99.76 GB 0.6 0.1 0.1 0.0 0.1 0.1 858.0 1.0 114.8 114.8 0.52 0.51 4 0.129 263K 0 0.0 0.0
L7 61356/0 758.40 GB 0.0 0.0 0.0 0.0 0.0 0.0 758.4 0.0 0.0 0.0 0.00 0.00 0 0.000 0 0 0.0 0.0
Sum 68531/4 875.96 GB 0.0 709.0 115.6 593.4 1585.0 991.6 4652.3 1.8 46.8 104.6 15517.21 14725.05 117648 0.132 3228M 0 0.0 0.0

Uptime(secs): 12858.4 total, 20.0 interval
Flush(GB): cumulative 878.339, interval 1.203
AddFile(GB): cumulative 0.000, interval 0.000
AddFile(Total Files): cumulative 0, interval 0
AddFile(L0 Files): cumulative 0, interval 0
AddFile(Keys): cumulative 0, interval 0
Cumulative compaction: 1585.01 GB write, 126.22 MB/s write, 709.03 GB read, 56.46 MB/s read, 15517.2 seconds
Stalls(count): 26163 level0_slowdown, 26055 level0_slowdown_with_compaction, 0 level0_numfiles, 0 level0_numfiles_with_compaction, 55628 stop for pending_compaction_bytes, 9343 slowdown for pending_compaction_bytes, 0 memtable_compaction,
0 memtable_slowdown, interval 62 total count

** DB Stats **
Uptime(secs): 12858.4 total, 20.0 interval
Cumulative writes: 0 writes, 3999M keys, 0 commit groups, 0.0 writes per commit group, ingest: 1624.01 GB, 129.33 MB/s
Cumulative WAL: 0 writes, 0 syncs, 0.00 writes per sync, written: 0.00 GB, 0.00 MB/s
Cumulative stall: 00:47:45.976 H:M:S, 22.3 percent
```

Compaction IO stats from test end for the hacked binary show that only trivial move is used:
```
Level Files Size Score Read(GB) Rn(GB) Rnp1(GB) Write(GB) Wnew(GB) Moved(GB) W-Amp Rd(MB/s) Wr(MB/s) Comp(sec) CompMergeCPU(sec) Comp(cnt) Avg(sec) KeyIn KeyDrop Rblob(GB) Wblob(GB)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
L0 18/1 155.06 MB 4.2 0.0 0.0 0.0 878.3 878.3 0.0 1.0 0.0 77.3 11640.79 8381.25 104400 0.112 0 0 0.0 0.0
L2 34/3 292.91 MB 4.2 0.0 0.0 0.0 0.0 0.0 585.5 0.0 0.0 0.0 0.00 0.00 0 0.000 0 0 0.0 0.0
L3 25/3 215.37 MB 1.0 0.0 0.0 0.0 0.0 0.0 841.3 0.0 0.0 0.0 0.00 0.00 0 0.000 0 0 0.0 0.0
L4 179/1 1.51 GB 1.0 0.0 0.0 0.0 0.0 0.0 873.1 0.0 0.0 0.0 0.00 0.00 0 0.000 0 0 0.0 0.0
L5 1426/0 12.00 GB 1.0 0.0 0.0 0.0 0.0 0.0 875.6 0.0 0.0 0.0 0.00 0.00 0 0.000 0 0 0.0 0.0
L6 11412/0 96.01 GB 1.0 0.0 0.0 0.0 0.0 0.0 864.1 0.0 0.0 0.0 0.00 0.00 0 0.000 0 0 0.0 0.0
L7 91303/0 768.14 GB 0.0 0.0 0.0 0.0 0.0 0.0 768.1 0.0 0.0 0.0 0.00 0.00 0 0.000 0 0 0.0 0.0
Sum 104397/8 878.30 GB 0.0 0.0 0.0 0.0 878.3 878.3 4807.7 1.0 0.0 77.3 11640.79 8381.25 104400 0.112 0 0 0.0 0.0

Uptime(secs): 19871.4 total, 20.0 interval
Flush(GB): cumulative 878.322, interval 0.412
AddFile(GB): cumulative 0.000, interval 0.000
AddFile(Total Files): cumulative 0, interval 0
AddFile(L0 Files): cumulative 0, interval 0
AddFile(Keys): cumulative 0, interval 0
Cumulative compaction: 878.32 GB write, 45.26 MB/s write, 0.00 GB read, 0.00 MB/s read, 11640.8 seconds
Stalls(count): 147247 level0_slowdown, 107452 level0_slowdown_with_compaction, 0 level0_numfiles, 0 level0_numfiles_with_compaction, 0 stop for pending_compaction_bytes, 0 slowdown for pending_compaction_bytes, 0 memtable_compaction, 115
memtable_slowdown, interval 205 total count

** DB Stats **
Uptime(secs): 19871.4 total, 20.0 interval
Cumulative writes: 0 writes, 3999M keys, 0 commit groups, 0.0 writes per commit group, ingest: 1623.98 GB, 83.69 MB/s
Cumulative WAL: 0 writes, 0 syncs, 0.00 writes per sync, written: 0.00 GB, 0.00 MB/s
Cumulative stall: 01:47:12.946 H:M:S, 32.4 percent
```

Perf results from test end:
```
# for the as-is binary
fillseq : 3.215 micros/op 311034 ops/sec; 124.6 MB/s
Microseconds per write:
Count: 4000000000 Average: 3.2151 StdDev: 0.20
Min: 0 Median: 0.5291 Max: 209052317
Percentiles: P50: 0.53 P75: 0.79 P99: 3.55 P99.9: 9.51 P99.99: 2464.22

# for the hacked binary
fillseq : 4.969 micros/op 201240 ops/sec; 80.6 MB/s
Microseconds per write:
Count: 4000000000 Average: 4.9692 StdDev: 0.17
Min: 0 Median: 0.5314 Max: 369655
Percentiles: P50: 0.53 P75: 0.80 P99: 3.59 P99.9: 8.88 P99.99: 3929.80
```