Cartesian clone type definition is wrong

What happened?

After #13168, the generated TypeScript definitions for the static clone methods are incorrect. Methods are extended to accept undefined and return undefined in that case, but TypeScript will throw an error on this with skipLibCheck: false.

TS2322: Type 'undefined' is not assignable to type 'Cartesian3'.
    102 |   static clone(cartesian, result) {
    103 |     if (!defined(cartesian)) {
  > 104 |       return undefined;
        |       ^^^^^^
    105 |     }
    106 |     if (!defined(result)) {
    107 |       return new Cartesian3(cartesian.x, cartesian.y, cartesian.z);

https://github.com/CesiumGS/cesium/blob/2428f04ac54f896b975a4fe1b90319feb62e080a/packages/engine/Source/Core/Cartesian2.js#L58-L76

Reproduction steps

Sandcastle example

No response

Environment

CesiumJS Version: 1.139.0

Start with packages/engine/Source/Core/Cartesian2.js around lines 58-76 and inspect how the static clone methods produce their generated TypeScript definitions. Run the TypeScript check with skipLibCheck set to false and confirm the clone definitions accept undefined and represent an undefined return without TS2322 errors.