Filtering reagents (#18211)

* Making it work

* Refactoring

* Autoformat revert

* Implementing suggestions

* Changed to file scoped namespaces.

Content.Client/Guidebook/GuideEntry.cs

@@ -29,6 +29,11 @@ public class GuideEntry
     [DataField("children", customTypeSerializer:typeof(PrototypeIdListSerializer<GuideEntryPrototype>))]
     public List<string> Children = new();
 
+    /// <summary>
+    ///     Enable filtering of items.
+    /// </summary>
+    [DataField("filterEnabled")] public bool FilterEnabled = default!;
+
     /// <summary>
     ///     Priority for sorting top-level guides when shown in a tree / table of contents.
     ///     If the guide is the child of some other guide, the order simply determined by the order of children in <see cref="Children"/>.