Bundles no longer available without enabling feature flag

Up until 1.21 the Bundle item was not locked behind the bundle experiment, only its recipe was. That's important because many data packs (such as the popular VanillaTweaks) added a recipe for the bundle to make it available in survival. Since the bundle experiment started receiving updates again, the bundle item itself is no longer available (e.g. via /give @p minecraft:bundle), which may be problematic when updating from 1.21(.1) to 1.21.2 eventually, if the bundle stays experimental in that version.