Replace Properties with Map<String, String> in Exporters interfaces

[karindev]

Fixes #6419

This makes changes to the 4.0 branch since the interface is already modified due to other changes.

Changes proposed in this pull request:

• Uses of Properties are replaced with Map<String, String> in the export() method of Exporters interfaces
• The classes implementing the interfaces are updated to match
• Methods exportRows() and countColumnRows() CustomizableTabularExporterUtilities are also changed to use Map<String, String> to accommodate the change
• Unit tests are updated to match all changed code and mocking is removed where unnecessary

[wetneb]

Thanks a lot for this!
I think I intuitively agree with the idea that it's worth doing this sort of change on the occasion of a larger change of interface, so adding it on top of the data model changes feels right in that sense. On the other hand there is also a case for keeping breaking changes as atomic as possible and giving people the opportunity to migrate gradually. We are currently discussing how to schedule such changes on the forum:
https://forum.openrefine.org/t/scheduling-breaking-changes-we-have-on-our-radar/1410/4

In the light of this discussion, I would keep this PR open (probably for a long time) until we have some clarity on how we proceed.
From my side, I would like to express my support to your approach and my gratitude for your work - even if it might not be reflected in the formal status of this PR as soon as I would wish!