Hands management element (#78887)

## About The Pull Request

Places "setting up being able to use hands" into an element so it can be
easily applied to non-carbon mobs.

## Why It's Good For The Game

This is one of the last roadblocks for basic mob implementation and
people were intimidated by it but it turns out this shit is easy, 90% of
this code is already just on `living` and I put a little bit more there.
The element _really_ only handles stuff like dropping items on death,
picking things up rather than biting them, and adding examine text.

This also removes some copy/pasted code between `simple_animal` and
`carbon` and unifies some behaviours which were implemented for some
dextrous simple animals but not others.

Changes to give Ian a single hand representing his mouth will come at a
later date.

## Changelog

🆑
qol: You can now see what drones and gorillas are holding by examining
them.
admin: It's now easier to give handless mobs hands by applying the
"dextrous" element.
balance: Spiders and Bears can now climb railings (you know if... they'd
rather do that than destroy them).
/🆑

code/modules/mob/living/basic/basic.dm

@@ -285,6 +285,21 @@
 		return last_icon_state
 	return null
 
+/mob/living/basic/put_in_hands(obj/item/I, del_on_fail = FALSE, merge_stacks = TRUE, ignore_animation = TRUE)
+	. = ..()
+	if (.)
+		update_held_items()
+
+/mob/living/basic/update_held_items()
+	if(isnull(client) || isnull(hud_used) || hud_used.hud_version == HUD_STYLE_NOHUD)
+		return
+	var/turf/our_turf = get_turf(src)
+	for(var/obj/item/held in held_items)
+		var/index = get_held_index_of_item(held)
+		SET_PLANE(held, ABOVE_HUD_PLANE, our_turf)
+		held.screen_loc = ui_hand_position(index)
+		client.screen |= held
+
 /mob/living/basic/get_body_temp_heat_damage_limit()
 	return maximum_survivable_temperature