this eliminates feedback loops during client-initiated slot changes, and also makes it possible to have a SlotChangeAction anonymous from its initiator.
the useHeldItem() sets the using-item flag back to true immediately after consumeHeldItem() sets it to false, which caused this bug.
stable has the same problem, but the effects don't show due to a well timed MobEquipmentPacket (a happy accident).
often we throw out actions that have no value, which can lead to an empty transaction and re-syncing the inventory. This happens every time we interact with the creative inventory in 1.13+, which causes items to appear to vanish when taking them from the creative menu.
The correct fix for this is to resend only the slots affected by SlotChangeActions, but this fix will suffice for now without rewriting everything.
