return to the character screeen. And other related improvements.
* Uid now optional when removing an entity from IdMaps since that Uid
may have been transferred to the new entity created when the client
exits "in-game".
* Added notes about making sure to update the CharacterId mapping when
changing the `kind` field of `Presence`.
* Add a parameter to `delete_entity_recorded` that indicates whether it
is being called from `handle_exit_ingame` and that provides the `Uid`
that was removed from the entity so that we can more explicitly and
correctly handle that case.
* We now add the Uid of the client to the deleted entities list when it
exits "ingame". (still need to rework code so that the client doesn't
delete its own entity).
* Improved integration of possession code with ForceUpdate logic.
* Don't remove `Presence` component from old entity in possession so
that deleting that entity will properly handle updating the
CharacterId unmapping (if the old entity isn't going to be deleted we
still remove the `Presence` component so that it doesn't keep terrain
loaded).
* Added a couple TODOs on existing tangential things I noticed.
other changes that already occured that tick.
Also get terrain/block change resources from the ecs once to avoid the
overhead of fetching them from the ecs (and aquiring/releasing runtime
borrow).
* Added `LootOwner` component used to indicate that an `ItemDrop` entity is owned by another entity
* A loot winner is now calculated after EXP allocation using the EXP per entity for weighted chance distribution
* Used existing Inventory Full overitem text to show "Owned by {player} for {seconds}secs" when a pickup fails due to a loot ownership check
* Updated agent code to take into account loot ownership when searching for `ItemDrop` targets to pick up
* Added `loot` ECS system to clear expired loot ownerships
