Ports CM wall leaning. (#21076)

All credit to the original coders, I only did minimal work to make it
work with Aurora code.

Something nice to steal would be the density rework, but that's for the
future.


https://github.com/user-attachments/assets/582edb20-5d86-4465-99bf-e4cec73c104a

---------

Co-authored-by: Matt Atlas <liermattia@gmail.com>

code/modules/mob/living/living.dm

@@ -678,6 +678,7 @@ default behaviour is:
 /mob/living/proc/execute_resist()
 
 	if(!incapacitated(INCAPACITATION_KNOCKOUT) && canClick())
+		SEND_SIGNAL(src, COMSIG_MOB_RESISTED)
 		resist_grab()
 		if(!weakened)
 			process_resist()