fix: move utility types out of .d.ts file to fix exported declaration files (#6315)

src/element/mutateElement.ts

@@ -5,6 +5,7 @@ import { getSizeFromPoints } from "../points";
 import { randomInteger } from "../random";
 import { Point } from "../types";
 import { getUpdatedTimestamp } from "../utils";
+import { Mutable } from "../utility-types";
 
 type ElementUpdate<TElement extends ExcalidrawElement> = Omit<
   Partial<TElement>,