Directory should be relative

[koppor]

1. Create C:\temp\jabref-tests\pr-13029
2. Open JabRef
3. New library
4. Save at C:\temp\jabref-tests\pr-13029\test.bib
5. Menu "Libarry". Select "Library properties"
6. Create and select folder "pdfs"
   
7. See that C:\temp\jabref-tests\pr-13029\pdfs is stored

Expected: pdfs is stored.

Reason: It is a sub folder of the current path.

Tasks:

1. After browsing: Path is made relative to .bib file
2. Add button "Make absolute" next to each directory, converting the selected path to an absolute path
   
3. The button is disabled if the path is already absolute

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This is a follow-up to #13029. There, one can find out about the code places.

[paudelritij]

/assign-me

[github-actions]

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