Customize save order in .layout

[calixtus]

As discussed in #12220 the .layout subsystem could provide some way to override the preferences save order.

[Siedlerchr]

Well, the export save order in the preferences is exactly for exports and thus affects the export using layout files. This is intended.

[koppor]

Documentation: https://docs.jabref.org/collaborative-work/export

If we have more use cases than single exports, we can discuss further.

The idea refs #8701 somehow. There, all settings concerdings a library were wished to be contained in the library itself - to make it portable. -- However, I see the .layouts differently.

[koppor]

Related (follow-up) issue: https://github.com/JabRef/jabref-issue-melting-pot/issues/700?notification_referrer_id=NT_kwDOABTafrMxMzU0NjgxMTQ2ODoxMzY2NjU0