Datumize tendon behavior, make tendon snapping more consistent (#11773)

code/modules/spell_system/spells/spell_list/others/generic/mend.dm

@@ -67,9 +67,9 @@
 			E.stage = 0
 			return 1
 
-		if(E.status & ORGAN_TENDON_CUT)
+		if(istype(E.tendon) && !E.tendon.intact)
 			to_chat(user, "<span class='notice'>You place your hands over [target]'s [E.name], joining the two ends of their [E.tendon_name] in the process.</span>")
-			E.status &= ~ORGAN_TENDON_CUT
+			E.tendon.heal()
 			return 1
 
 		for(var/obj/item/organ/I in E.internal_organs)
@@ -79,4 +79,4 @@
 				return 1
 
 		to_chat(user, "<span class='notice'>You can find nothing within \the [target]'s [E.name] to mend.</span>")
-		return 1
+		return 1