MapKit JS 6: CollisionMode alias warns, clustering ignores displayPriority

In MapKit JS 6, reading mapkit.Annotation.CollisionMode (and Annotation.DisplayPriority) still works but each access logs a console.warn deprecation; use mapkit.AnnotationCollisionMode.None (value "none") instead. Annotations sharing a clusteringIdentifier are clustered whenever they overlap regardless of displayPriority (only selected or collision-none ones are skipped), so lowering one pin's priority does not make it give way to others in the same cluster group; a cluster takes its highest-priority member's priority and sits at the members' centroid. map.region is visibleMapRect.toCoordinateRegion(): its centre is the Mercator midpoint, so centre plus or minus half the latitude span is not the visible box at country-wide zooms. Verified by reading the 6.0.x CDN bundle as text.