Rejigging Item slots (#4933)

* itemslot overhaul

* remove "shared" prefix

* handle component shutdown

* comments, cleanup, tests

* comments and minor tweak

* rename ItemSlotManagerState

* fix swapping

* fix merge

* Add ItemSlot verb text override

* fix merge  (IEntity -> entityUid)

* Fix merge (LabelSystem)

* Fix merge (nuke disk)

* fix test

Resources/Textures/Interface/VerbIcons/drop.svg.192dpi.png.yml

@@ -0,0 +1,4 @@
+# For now, this icon is literally just the pickup icon rotated 180 degrees.
+# But maybe this will change in the future?
+sample:
+  filter: true