synchronize more on quest visibility updates

[westnordost]

fixes #5545

[Helium314]

Looks good!
Though now I'm pondering whether it would also be a problem if onUpdated overtakes onReplacedForBbox while quests for the bbox are being created. Anyway, this is not what happened in the log provided in #5545 (comment)

[westnordost]

Ehm, which class?

[Helium314]

OsmQuestController.mapDataSourceListener
If we assume persisting elements is done, and onReplacedForBBox is called, then could it be bad if onUpdated if called while onReplacedForBBox is in createQuestsForBBox?
But maybe we should just work on problems that actually occurred, and think about this only if the quest-asked-again issue comes up again.

[westnordost]

I think this is covered by the fact that the MapDataWithElementsSource will replay any updates done while replacing the bbox.