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/Standing/StandingStateComponent.cs

@@ -0,0 +1,54 @@
+using System;
+using Content.Shared.EffectBlocker;
+using Content.Shared.NetIDs;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Players;
+using Robust.Shared.Serialization;
+using Robust.Shared.Serialization.Manager.Attributes;
+using Robust.Shared.ViewVariables;
+
+namespace Content.Shared.Standing
+{
+    [RegisterComponent]
+    public sealed class StandingStateComponent : Component, IEffectBlocker
+    {
+        public override string Name => "StandingState";
+
+        public override uint? NetID => ContentNetIDs.STANDING_STATE;
+
+        [ViewVariables(VVAccess.ReadWrite)]
+        [DataField("downSoundCollection")]
+        public string? DownSoundCollection { get; } = "BodyFall";
+
+        [ViewVariables]
+        [DataField("standing")]
+        public bool Standing { get; set; } = true;
+
+        public bool CanFall() => Standing;
+
+        public override ComponentState GetComponentState(ICommonSession player)
+        {
+            return new StandingComponentState(Standing);
+        }
+
+        public override void HandleComponentState(ComponentState? curState, ComponentState? nextState)
+        {
+            base.HandleComponentState(curState, nextState);
+            if (curState is not StandingComponentState state) return;
+
+            Standing = state.Standing;
+        }
+
+        // I'm not calling it StandingStateComponentState
+        [Serializable, NetSerializable]
+        private sealed class StandingComponentState : ComponentState
+        {
+            public bool Standing { get; }
+
+            public StandingComponentState(bool standing) : base(ContentNetIDs.STANDING_STATE)
+            {
+                Standing = standing;
+            }
+        }
+    }
+}