Adds hand labelers (#4903)

* Adds hand labelers

* Removes unnecessary thing

* Docs

* Reverts some changes

* Addresses comments and adds inhand sprites

* Addressed comments

Co-authored-by: Watermelon914 <3052169-Watermelon914@users.noreply.gitlab.com>

Content.Shared/HandLabeler/SharedHandLabelerComponent.cs

@@ -0,0 +1,41 @@
+using System;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.HandLabeler
+{
+    /// <summary>
+    /// Key representing which <see cref="BoundUserInterface"/> is currently open.
+    /// Useful when there are multiple UI for an object. Here it's future-proofing only.
+    /// </summary>
+    [Serializable, NetSerializable]
+    public enum HandLabelerUiKey
+    {
+        Key,
+    }
+
+    /// <summary>
+    /// Represents a <see cref="HandLabelerComponent"/> state that can be sent to the client
+    /// </summary>
+    [Serializable, NetSerializable]
+    public class HandLabelerBoundUserInterfaceState : BoundUserInterfaceState
+    {
+        public string CurrentLabel { get; }
+
+        public HandLabelerBoundUserInterfaceState(string currentLabel)
+        {
+            CurrentLabel = currentLabel;
+        }
+    }
+
+    [Serializable, NetSerializable]
+    public class HandLabelerLabelChangedMessage : BoundUserInterfaceMessage
+    {
+        public string Label { get; }
+
+        public HandLabelerLabelChangedMessage(string label)
+        {
+            Label = label;
+        }
+    }
+}