Adds ghost drag-dropping into mobs.

A port of https://github.com/tgstation/-tg-station/pull/8957.
This is so slick, you have no idea.

code/modules/admin/admin.dm

@@ -1353,3 +1353,36 @@ proc/formatLocation(location)
 
 proc/formatPlayerPanel(var/mob/U,var/text="PP")
 	return "<A HREF='?_src_=holder;adminplayeropts=\ref[U]'>[text]</A>"
+
+//Credit to MrStonedOne from TG for this QoL improvement
+//returns 1 to let the dragdrop code know we are trapping this event
+//returns 0 if we don't plan to trap the event
+/datum/admins/proc/cmd_ghost_drag(var/mob/dead/observer/frommob, var/mob/living/tomob)
+
+	//if we couldn't do it manually, we can't do it here - the 0 means no message is displayed for failure
+	if (!check_rights(R_VAREDIT, 0))
+		return 0
+
+	if (!frommob.ckey)
+		return 0
+
+	var/question = ""
+	if (tomob.ckey)
+		question = "This mob already has a user ([tomob.key]) in control of it! "
+	question += "Are you sure you want to place [frommob.name]([frommob.key]) in control of [tomob.name]?"
+	if(alert(question, "Place ghost in control of mob?", "Yes", "No") != "Yes")
+		return 1
+
+	if (!frommob || !tomob) //make sure the mobs don't go away while we waited for a response
+		return 1
+
+	tomob.ghostize(0) //boot the old mob out
+
+	message_admins("<span class='adminnotice'>[key_name_admin(usr)] has put [frommob.ckey] in control of [tomob.name].</span>")
+	log_admin("[key_name(usr)] stuffed [frommob.ckey] into [tomob.name].")
+	feedback_add_details("admin_verb","CGD")
+	tomob.ckey = frommob.ckey
+	qdel(frommob)
+	return 1
+
+

code/modules/mob/dead/observer/login.dm

@@ -10,3 +10,13 @@
 					src << 'sound/effects/adminhelp.ogg'
 					src << "<b><font color = #330033><font size = 3>Your corpse has been placed into a cloning scanner. Return to your body if you want to be resurrected/cloned!</b> (Verbs -> Ghost -> Re-enter corpse)</font color>"
 	canclone = null
+
+/mob/dead/observer/MouseDrop(atom/over)
+	if(!usr || !over)
+		return
+
+	if (isobserver(usr) && usr.client.holder && isliving(over))
+		if (usr.client.holder.cmd_ghost_drag(src,over))
+			return
+
+	return ..()