Investigate points disk usage reduction on NYC Taxis between 2020-11-01 and 2021-09-24 [LUCENE-10124]

There's been a 35% ⚠ reduction of disk usage for points on the NYC Taxis benchmark some time between 2020-11-01 and 2021-09-24 when I make disk usage for points work again. I can't think of a change that would have decreased disk usage by so much.

https://home.apache.org/\~mikemccand/lucenebench/sparseResults.html#index_size_parts

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Migrated from [LUCENE-10124](https://issues.apache.org/jira/browse/LUCENE-10124) by Adrien Grand (@jpountz), updated Sep 29 2021

Start with the NYC Taxis benchmark results at sparseResults.html#index_size_parts and compare the points disk-usage data between 2020-11-01 and 2021-09-24. Trace the Lucene changes in that interval that could affect points storage, then document the cause of the reported 35% reduction and confirm it against the benchmark.

Written by the indexing model from the issue text.