Remove string appearance keys (#10114)

Content.Shared/Toggleable/ToggleableLightVisuals.cs

@@ -4,8 +4,23 @@ namespace Content.Shared.Toggleable;
 
 // Appearance Data key
 [Serializable, NetSerializable]
-public enum ToggleableLightVisuals
+public enum ToggleableLightVisuals : byte
 {
     Enabled,
     Color
 }
+
+/// <summary>
+///     Generic sprite layer keys.
+/// </summary>
+[Serializable, NetSerializable]
+public enum LightLayers : byte
+{
+    Light,
+
+    /// <summary>
+    ///     Used as a key for generic unshaded layers. Not necessarily related to an entity with an actual light source.
+    ///     Use this instead of creating a unique single-purpose "unshaded" enum for every visualizer. 
+    /// </summary>
+    Unshaded,
+}