Let body parts in organs inventory affect abilities of actors

Let actors start with a few legs/arms/tentacles in inventory. If a leg is missing, the actor can't kick in combat, has trouble moving, etc.. Let body parts be targetable in combat. If a body part is critically wounded, it's removed from the inventory. If it's later regrown/replaced by an implant/etc. a new item is added to the inventory. The body parts in the inventory are displayed separately and some operations are restricted (e.g., dropping an arm is forbidden and picking up a severed arm does not re-attach it). Since body parts are items, they are specified in game content, just as any other item (this bit is already done and they are specified in ItemKindOrgan).

Start with the existing ItemKindOrgan game-content definition and trace how organ items are represented in actors' inventories. Define the inventory, combat targeting, movement, regrowth, replacement, display, and restricted-operation behavior described in the issue, then verify that missing and restored body parts affect actors as specified.