Seal/abstract/virtual everything (#6739)

Content.Shared/Slippery/NoSlipComponent.cs

@@ -3,7 +3,7 @@ using Robust.Shared.GameObjects;
 namespace Content.Shared.Slippery
 {
     [RegisterComponent]
-    public class NoSlipComponent : Component
+    public sealed class NoSlipComponent : Component
     {
     }
 }

Content.Shared/Slippery/SharedSlipperySystem.cs

@@ -159,7 +159,7 @@ namespace Content.Shared.Slippery
     /// <summary>
     ///     Raised on an entity to determine if it can slip or not.
     /// </summary>
-    public class SlipAttemptEvent : CancellableEntityEventArgs, IInventoryRelayEvent
+    public sealed class SlipAttemptEvent : CancellableEntityEventArgs, IInventoryRelayEvent
     {
         public SlotFlags TargetSlots { get; } = SlotFlags.FEET;
     }

Content.Shared/Slippery/SlipperyComponent.cs

@@ -161,7 +161,7 @@ namespace Content.Shared.Slippery
     }
 
     [Serializable, NetSerializable]
-    public class SlipperyComponentState : ComponentState
+    public sealed class SlipperyComponentState : ComponentState
     {
         public float ParalyzeTime { get; }
         public float IntersectPercentage { get; }