Introduce some functional programming techniques

src/file/drawing/floating/simple-pos.ts

@@ -2,12 +2,12 @@
 import { XmlAttributeComponent, XmlComponent } from "file/xml-components";
 
 interface ISimplePosAttributes {
-    x: number;
-    y: number;
+    readonly x: number;
+    readonly y: number;
 }
 
 class SimplePosAttributes extends XmlAttributeComponent<ISimplePosAttributes> {
-    protected xmlKeys = {
+    protected readonly xmlKeys = {
         x: "x",
         y: "y",
     };