Move ActorEquip and related structs to GameData.

Penumbra.GameData/Structs/StainId.cs

@@ -0,0 +1,29 @@
+using System;
+
+namespace Penumbra.GameData.Structs
+{
+    public readonly struct StainId : IEquatable<StainId>
+    {
+        public readonly byte Value;
+
+        public StainId( byte value )
+            => Value = value;
+
+        public static implicit operator StainId( byte id ) => new( id );
+
+        public static explicit operator byte( StainId id )
+            => id.Value;
+
+        public override string ToString()
+            => Value.ToString();
+
+        public bool Equals( StainId other )
+            => Value == other.Value;
+
+        public override bool Equals( object? obj )
+            => obj is StainId other && Equals( other );
+
+        public override int GetHashCode()
+            => Value.GetHashCode();
+    }
+}