index upgrade tool for /dev-tools [LUCENE-2893]

we change the index format from time to time, and people tracking trunk have to re-index.

I think we should put a (unsupported, scary) tool in /dev-tools that uses the PreflexRW Codec to
serialize the index to a 3.0 index (with your old trunk version), you can then deserialize it back
with the newer trunk version, to the newest StandardCodec.

this won't prevent all reindexes, but would work for changes under codec control.

mainly though, I think we could somehow add undeleteAll + this tool + apply deletes to prevent
the painful reindexing of luceneutil benchmarking indexes :)

---
Migrated from [LUCENE-2893](https://issues.apache.org/jira/browse/LUCENE-2893) by Robert Muir (@rmuir), updated Nov 20 2020
Attachments: [LUCENE-2893.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-2893/LUCENE-2893.patch)
Linked issues:
- #4155