Move ActorEquip and related structs to GameData.

Penumbra.GameData/Structs/SetId.cs

@@ -0,0 +1,23 @@
+using System;
+
+namespace Penumbra.GameData.Structs
+{
+    public readonly struct SetId : IComparable<SetId>
+    {
+        public readonly ushort Value;
+
+        public SetId( ushort value )
+            => Value = value;
+
+        public static implicit operator SetId( ushort id ) => new(id);
+
+        public static explicit operator ushort( SetId id )
+            => id.Value;
+
+        public override string ToString()
+            => Value.ToString();
+
+        public int CompareTo( SetId other )
+            => Value.CompareTo( other.Value );
+    }
+}