Change lucene index path to have sub directories

[koppor]

Follow-up to #9584. Fixes https://github.com/JabRef/jabref-issue-melting-pot/issues/93.

Lucene-Index is now stored in lucence/<version>.

├───backups
├───logs
│   ├───100.0.0
│   ├───5.10--2023-04-06--0111d59
│   └───5.9--2023-01-04--bc3b9892f
├───lucene
│   └───95
│       ├───-369469544
│       └───40622060
└───ssl

Thus, %APPDATA%\..\Local\org.jabref looks more clean to the user

Discussion was done at #9676.

Upgrade from lucene94 to 95 was done after release of JabRef v5.9 and thus this change does not affect users basing on the release version. They will encounter a re-index in all cases.

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5. Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
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[Siedlerchr]

Use private static final String FILE_SEPARATOR = System.getProperty("file.separator");
from OS.java in

[koppor]

[koppor]

I removed the unused variable. I didn't want to be the first one using it. 😇

[Siedlerchr]

Then use the nio variant: String separator = FileSystems.getDefault().getSeparator();

[Siedlerchr]

see comment

[calixtus]

Os class has to be rewritten, unifying access to all filesystem and os variables

[Siedlerchr]

Os class has to be rewritten, unifying access to all filesystem and os variables

For that we have JabrefDeskop with the sublcaseses

[calixtus]

Yes, so JabrefDesktop needs to be fixed. I don't like calling appdirs or environment vars directly in this class. It should keep the level of abstraction.

[koppor]

I don't like calling appdirs or environment vars directly in this class. It should keep the level of abstraction.

Moved the code to NativeDesktop at 6148974 (#9887).

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[Siedlerchr]

Merging now as we have lucene 9.6 ugprade