Shared subfloor system (#3590)

* Shared subfloor system

Will also cull the broadphase for server a lot.

* Nullable subfloor

* Snapgrid nullable

* Actually use ComponentDependency

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Shared/GameObjects/Components/SubFloorHideComponent.cs

@@ -0,0 +1,72 @@
+#nullable enable
+using Robust.Shared.GameObjects;
+using Robust.Shared.Log;
+
+namespace Content.Shared.GameObjects.Components
+{
+    /// <summary>
+    /// Simple component that automatically hides the sibling
+    /// <see cref="ISpriteComponent" /> when the tile it's on is not a sub floor
+    /// (plating).
+    /// </summary>
+    /// <seealso cref="P:Content.Shared.Maps.ContentTileDefinition.IsSubFloor" />
+    [RegisterComponent]
+    public sealed class SubFloorHideComponent : Component
+    {
+        [ComponentDependency(nameof(OnAddSnapGrid))]
+        private SnapGridComponent? _snapGridComponent;
+
+        /// <inheritdoc />
+        public override string Name => "SubFloorHide";
+
+        /// <inheritdoc />
+        protected override void Startup()
+        {
+            base.Startup();
+
+            Owner.EntityManager.EventBus.RaiseEvent(EventSource.Local, new SubFloorHideDirtyEvent(Owner));
+        }
+
+        /// <inheritdoc />
+        protected override void Shutdown()
+        {
+            base.Shutdown();
+
+            if (Owner.Transform.Running == false)
+                return;
+
+            if (_snapGridComponent != null)
+            {
+                _snapGridComponent.OnPositionChanged -= SnapGridOnPositionChanged;
+            }
+
+            Owner.EntityManager.EventBus.RaiseEvent(EventSource.Local, new SubFloorHideDirtyEvent(Owner));
+        }
+
+        private void OnAddSnapGrid()
+        {
+            if (_snapGridComponent == null)
+            {
+                // Shouldn't happen but allows us to use nullables. OnPositionChanged needs to be componentbus anyway.
+                Logger.Error("Snapgrid was null for subfloor {Owner}");
+                return;
+            }
+            _snapGridComponent.OnPositionChanged += SnapGridOnPositionChanged;
+        }
+
+        private void SnapGridOnPositionChanged()
+        {
+            Owner.EntityManager.EventBus.RaiseEvent(EventSource.Local, new SubFloorHideDirtyEvent(Owner));
+        }
+    }
+
+    internal sealed class SubFloorHideDirtyEvent : EntityEventArgs
+    {
+        public IEntity Sender { get; }
+
+        public SubFloorHideDirtyEvent(IEntity sender)
+        {
+            Sender = sender;
+        }
+    }
+}