examine signature changed to include distance

- distance is INFINITE, 0, or a positive integer based on get_dist() between
the examiner and examinee's turfs when they are on the same Z. When the
examiner is dead or a ghost, distance is always 0.
- also updates /examine( implementations to use it!
- adds w_class_to_name proc for reusing "It is a X item." examine behavior.

code/modules/shieldgen/shield_diffuser.dm

@@ -67,8 +67,8 @@
 	alarm = round(max(alarm, duration))
 	update_icon()
 
-/obj/machinery/shield_diffuser/examine(var/mob/user)
+/obj/machinery/shield_diffuser/examine(mob/user, distance, infix, suffix)
 	. = ..()
 	. += "It is [enabled ? "enabled" : "disabled"]."
 	if(alarm)
-		. += "A red LED labeled \"Proximity Alarm\" is blinking on the control panel."
+		. += "A red LED labeled \"Proximity Alarm\" is blinking on the control panel."