Fix antag info panel on body loss, also some sanity (#63976)

Losing your body as an antag will correctly remove the antag info panel from the body
    Gaining a new body as an antag will give the panel to the new body
    Adds some sanity checks to ensure no one who doesn't need to be seeing the panel can use it

Fixes #63303 (Antag Panel lost, upon switching to another Golem body (and considered dead for others))

You can see your objectives after being brain transplanted as an antag

code/modules/antagonists/_common/antag_datum.dm

@@ -94,6 +94,8 @@ GLOBAL_LIST_EMPTY(antagonists)
 	remove_innate_effects(old_body)
 	if(!soft_antag && old_body && old_body.stat != DEAD && !LAZYLEN(old_body.mind?.antag_datums))
 		old_body.remove_from_current_living_antags()
+	info_button.Remove(old_body)
+	info_button.Grant(new_body)
 	apply_innate_effects(new_body)
 	if(!soft_antag && new_body.stat != DEAD)
 		new_body.add_to_current_living_antags()
@@ -141,7 +143,7 @@ GLOBAL_LIST_EMPTY(antagonists)
 	if(!owner.current)
 		CRASH("[src] ran on_gain() on a mind without a mob")
 	if(ui_name)//in the future, this should entirely replace greet.
-		info_button = new(owner.current, src)
+		info_button = new(src)
 		info_button.Grant(owner.current)
 	if(!silent)
 		greet()
@@ -477,16 +479,27 @@ GLOBAL_LIST_EMPTY(antagonists)
 /datum/action/antag_info
 	name = "Open Antag Information:"
 	button_icon_state = "round_end"
-	var/datum/antagonist/antag_datum
 
-/datum/action/antag_info/New(Target, datum/antagonist/antag_datum)
+/datum/action/antag_info/New(Target)
 	. = ..()
-	src.antag_datum = antag_datum
-	name += " [antag_datum.name]"
+	name += " [target]"
 
 /datum/action/antag_info/Trigger()
-	if(antag_datum)
-		antag_datum.ui_interact(owner)
+	. = ..()
+	if(!.)
+		return
+
+	target.ui_interact(owner)
 
 /datum/action/antag_info/IsAvailable()
+	if(!target)
+		stack_trace("[type] was used without a target antag datum!")
+		return FALSE
+	. = ..()
+	if(!.)
+		return
+	if(!owner.mind)
+		return FALSE
+	if(!(target in owner.mind.antag_datums))
+		return FALSE
 	return TRUE