Is your feature request related to a problem? Please describe

See parent issue for details

Describe the solution you'd like

This issue mostly involves cleaning up uses of LegacyESVersion.fromString() that can be safely replaced with uses of Version.fromString().

That is, they're not really referring to Elasticsearch versions at all. They're just talking about version math.

I could be mistaken, but I think this covers most (all?) references to LegacyESVersion.fromString() outside of the reindex module. The reindex module is covered by a separate issue, because it really does need to know what Elasticsearch version it's talking to.

Related component

Other

Describe alternatives you've considered

No response

Additional context

No response