Abstract away or eliminate most of the mutation of the Elements array (#955)

src/types.ts

@@ -1,7 +1,9 @@
 import { ExcalidrawElement, PointerType } from "./element/types";
 import { SHAPES } from "./shapes";
+import { Point as RoughPoint } from "roughjs/bin/geometry";
 
 export type FlooredNumber = number & { _brand: "FlooredNumber" };
+export type Point = Readonly<RoughPoint>;
 
 export type AppState = {
   draggingElement: ExcalidrawElement | null;