Fix Laying Down Bugs (Simple-Station#933)

# Description

This fixes prediction issues, both where pressing the Lay down key
causes all entities on your screen to glitch and lay down, as well as
the bug where upon receiving ANY movement input, a player would be
visually changed on their screen to be laying down.

# Changelog

:cl:
- fix: Fixed issues with the LayingDownSystem. Laying down no longer
causes all entities on your screen to lay down at once. Using any
movement input no longer causes the character to appear to the player as
to be laying down.

Content.Client/Standing/LayingDownSystem.cs

@@ -1,4 +1,4 @@
-using Content.Shared.ActionBlocker;
+using Content.Shared.Buckle;
 using Content.Shared.Rotation;
 using Content.Shared.Standing;
 using Robust.Client.GameObjects;
@@ -11,8 +11,9 @@ public sealed class LayingDownSystem : SharedLayingDownSystem
 {
     [Dependency] private readonly IGameTiming _timing = default!;
     [Dependency] private readonly IEyeManager _eyeManager = default!;
+    [Dependency] private readonly StandingStateSystem _standing = default!;
     [Dependency] private readonly AnimationPlayerSystem _animation = default!;
-    [Dependency] private readonly ActionBlockerSystem _actionBlocker = default!;
+    [Dependency] private readonly SharedBuckleSystem _buckle = default!;
 
     public override void Initialize()
     {
@@ -26,7 +27,8 @@ public override void Initialize()
     private void OnMovementInput(EntityUid uid, LayingDownComponent component, MoveEvent args)
     {
         if (!_timing.IsFirstTimePredicted
-            || !_actionBlocker.CanMove(uid)
+            || !_standing.IsDown(uid)
+            || _buckle.IsBuckled(uid)
             || _animation.HasRunningAnimation(uid, "rotate")
             || !TryComp<TransformComponent>(uid, out var transform)
             || !TryComp<SpriteComponent>(uid, out var sprite)

Content.Shared/Standing/SharedLayingDownSystem.cs

@@ -40,7 +40,8 @@ public override void Shutdown()
 
     private void ToggleStanding(ICommonSession? session)
     {
-        if (session?.AttachedEntity == null
+        if (session is not { AttachedEntity: { Valid: true } uid } _
+            || !Exists(uid)
             || !HasComp<LayingDownComponent>(session.AttachedEntity)
             || _gravity.IsWeightless(session.AttachedEntity.Value))
             return;