Adds a Visualizer for the Gravity Generator (#2277)

* Adds Visualizer to GravityGenerator

* nullable

* snake bad

* -Reads layers from yaml
-Reads sprite states from yaml

* Fix GravityGridTest

Content.Client/GameObjects/Components/Gravity/GravityGeneratorVisualizer.cs

@@ -0,0 +1,69 @@
+#nullable enable
+using Content.Shared.GameObjects.Components.Gravity;
+using Robust.Client.GameObjects;
+using Robust.Shared.Interfaces.GameObjects;
+using Robust.Shared.Utility;
+using System;
+using System.Collections.Generic;
+using YamlDotNet.RepresentationModel;
+
+namespace Content.Client.GameObjects.Components.Gravity
+{
+    public class GravityGeneratorVisualizer : AppearanceVisualizer
+    {
+        private Dictionary<GravityGeneratorStatus, string> _spriteMap = new Dictionary<GravityGeneratorStatus, string>();
+
+        public override void InitializeEntity(IEntity entity)
+        {
+            base.InitializeEntity(entity);
+
+            if (!entity.TryGetComponent(out SpriteComponent? sprite))
+                return;
+
+            sprite.LayerMapReserveBlank(GravityGeneratorVisualLayers.Base);
+            sprite.LayerMapReserveBlank(GravityGeneratorVisualLayers.Core);
+        }
+
+        public override void LoadData(YamlMappingNode node)
+        {
+            base.LoadData(node);
+
+            // Get Sprites for each status
+            foreach (var status in (GravityGeneratorStatus[]) Enum.GetValues(typeof(GravityGeneratorStatus)))
+            {
+                if (node.TryGetNode(status.ToString().ToLower(), out var sprite))
+                {
+                    _spriteMap[status] = sprite.AsString();
+                }
+            }
+        }
+
+        public override void OnChangeData(AppearanceComponent component)
+        {
+            base.OnChangeData(component);
+
+            var sprite = component.Owner.GetComponent<SpriteComponent>();
+
+            if (component.TryGetData(GravityGeneratorVisuals.State, out GravityGeneratorStatus state))
+            {
+                if (_spriteMap.TryGetValue(state, out var spriteState))
+                {
+                    var layer = sprite.LayerMapGet(GravityGeneratorVisualLayers.Base);
+                    sprite.LayerSetState(layer, spriteState);
+                }
+            }
+
+            if (component.TryGetData(GravityGeneratorVisuals.CoreVisible, out bool visible))
+            {
+                var layer = sprite.LayerMapGet(GravityGeneratorVisualLayers.Core);
+                sprite.LayerSetVisible(layer, visible);
+            }
+        }
+
+        public enum GravityGeneratorVisualLayers
+        {
+            Base,
+            Core
+        }
+    }
+}