Core/Units: Rename and change Get/SetVisibility to use a bool value instead of an unnecessary enum

Also replace some SetVisibility hacks to directly call UpdateObjectVisibility

--HG--
branch : trunk

src/server/game/Spells/Auras/SpellAuraEffects.cpp

@@ -2924,8 +2924,8 @@ void AuraEffect::HandlePhase(AuraApplication const * aurApp, uint8 mode, bool ap
         target->SetPhaseMask(PHASEMASK_NORMAL, false);
 
     // need triggering visibility update base at phase update of not GM invisible (other GMs anyway see in any phases)
-    if (target->GetVisibility() != VISIBILITY_OFF)
-        target->SetVisibility(target->GetVisibility());
+    if (!target->IsVisible())
+        target->UpdateObjectVisibility();
 }
 
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