Refactor standing to be ECS (#4142)

* Refactor standing to be ECS

E C S B A B Y

* DONE

* FIX IT FIX IT FIX IT

* IsDown event

* Change to methods

* Fixes

* Address some reviews

* Last of the Mohicans

* Final fixes

* Fix tests

Content.Shared/MobState/State/SharedNormalMobState.cs

@@ -1,4 +1,7 @@
-#nullable enable
+using Content.Shared.Standing;
+using Robust.Shared.GameObjects;
+
+#nullable enable
 
 namespace Content.Shared.MobState.State
 {
@@ -9,6 +12,17 @@ namespace Content.Shared.MobState.State
     {
         protected override DamageState DamageState => DamageState.Alive;
 
+        public override void EnterState(IEntity entity)
+        {
+            base.EnterState(entity);
+            EntitySystem.Get<StandingStateSystem>().Stand(entity);
+
+            if (entity.TryGetComponent(out SharedAppearanceComponent? appearance))
+            {
+                appearance.SetData(DamageStateVisuals.State, DamageState.Alive);
+            }
+        }
+
         public override bool CanInteract()
         {
             return true;