feat(xanthous): Add a command to describe an item in the inventory

Add a new DescribeInventory command, bound to I, to prompt for an item
in the inventory (anywhere in the inventory, including wielded) and
display a (new) panel describing it in detail. This description includes
the description, the long description, and the item's physical
properties (volume, density, and weight).

Change-Id: Idc1a05ab16b4514728d42aa6b520f93bea807c07
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3227
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

users/grfn/xanthous/src/Xanthous/messages.yaml

@@ -24,7 +24,7 @@ entities:
 
 pickUp:
   menu: What would you like to pick up?
-  pickUp: You pick up the {{item.itemType.name}}
+  pickUp: You pick up the {{item.itemType.name}}.
   nothingToPickUp: "There's nothing here to pick up"
 
 cant:
@@ -101,6 +101,11 @@ read:
   nothing: "There's nothing there to read"
   result: "\"{{message}}\""
 
+inventory:
+  describe:
+    select: Select an item in your inventory to describe
+    nothing: You aren't carrying anything
+
 wield:
   nothing:
     - You aren't carrying anything you can wield