[WIP] Fix field formatter save actions throwing exception on autosave

[Siedlerchr]

Fixes #4958

In my opinion this is an ugly hack but still the only option without violating our architecture.
Problem is that the autocompleter has an input binding which is triggered whenever setField in BibEntry is called, in this case part of the apply save actions.
On autosave we have a Background thread in the BackupoManager which executes the saveDatabaseAction which itself executes the save actions.

Exectuted in a background thread:

jabref/src/main/java/org/jabref/logic/autosaveandbackup/BackupManager.java

Lines 120 to 124 in e83680f

	Charset charset = bibDatabaseContext.getMetaData().getEncoding().orElse(preferences.getDefaultEncoding());
	SavePreferences savePreferences = preferences.loadForSaveFromPreferences().withEncoding
	(charset).withMakeBackup(false);
	new BibtexDatabaseWriter(new AtomicFileWriter(backupPath, savePreferences.getEncoding()), savePreferences)
	.saveDatabase(bibDatabaseContext);

jabref/src/main/java/org/jabref/logic/exporter/BibDatabaseWriter.java

Lines 170 to 177 in e83680f

	// Write database entries.
	List<BibEntry> sortedEntries = getSortedEntries(bibDatabaseContext, entries, preferences);
	List<FieldChange> saveActionChanges = applySaveActions(sortedEntries, bibDatabaseContext.getMetaData());
	saveActionsFieldChanges.addAll(saveActionChanges);
	if (preferences.generateBibtexKeysBeforeSaving()) {
	List<FieldChange> keyChanges = generateBibtexKeys(bibDatabaseContext, sortedEntries);
	saveActionsFieldChanges.addAll(keyChanges);
	}

---

• Change in CHANGELOG.md described
• Tests created for changes
• Manually tested changed features in running JabRef
• Screenshots added in PR description (for bigger UI changes)
• Ensured that the git commit message is a good one
• Check documentation status (Issue created for outdated help page at help.jabref.org?)

[tobiasdiez]

I think we need a generic solution for this. Otherwise we run consistently in these threading issues and in the long term it's not a reliable solution to extract certain things that need to run on the javafx thread due to the bindings.

I would propose to create methods bindOnUI(Property A, Property B) and bindBidirectionalOnUI in BindingsHelper which bind A and B but changes are propagated on the JavaFX thread. The implementation probably needs to copy the builtin classes and change the update mechanism:
https://github.com/javafxports/openjdk-jfx/blob/develop/modules/javafx.base/src/main/java/javafx/beans/property/ObjectPropertyBase.java#L234
https://github.com/javafxports/openjdk-jfx/blob/51f12edf47adfe0529e8cea10f399f4525687d27/modules/javafx.base/src/main/java/com/sun/javafx/binding/BidirectionalBinding.java#L599