Fix map renderer error when painting decals with paths that start with /Textures (#16822)

Content.MapRenderer/Painters/DecalData.cs

@@ -2,17 +2,4 @@
 
 namespace Content.MapRenderer.Painters;
 
-public sealed class DecalData
-{
-    public DecalData(Decal decal, float x, float y)
-    {
-        Decal = decal;
-        X = x;
-        Y = y;
-    }
-
-    public Decal Decal;
-
-    public float X;
-    public float Y;
-}
+public readonly record struct DecalData(Decal Decal, float X, float Y);