feat(node): 使setWorldPosition方法的z参数变为可选参数

cocos/scene-graph/node.ts

@@ -59,7 +59,7 @@
 
 const idGenerator = new js.IDGenerator('Node');
 
 function getConstructor<T> (typeOrClassName: string | Constructor<T> | AbstractedConstructor<T>): Constructor<T> | AbstractedConstructor<T> | null | undefined {
     if (!typeOrClassName) {
         errorID(3804);
         return null;
@@ -316,7 +316,7 @@
         return null;
     }
 
     protected static _findComponents<T extends Component> (node: Node, constructor: Constructor<T> | AbstractedConstructor<T>, components: Component[]): void {
         const cls = constructor;
         const comps = node._components;
         // NOTE: internal rtti property
@@ -2616,15 +2616,19 @@
      * @param y Y axis position
      * @param z Z axis position
      */
-    public setWorldPosition(x: number, y: number, z: number): void;
+    public setWorldPosition(x: number, y: number, z?: number): void;
 
     public setWorldPosition (val: Vec3 | number, y?: number, z?: number): void {
         const worldPosition = this._pos;
 
         if (y === undefined) {
             Vec3.copy(worldPosition, val as Vec3);
         } else {
-            Vec3.set(worldPosition, val as number, y, z!);
+            if (z === undefined) {
+                z = worldPosition.z;
+            }
+
+            Vec3.set(worldPosition, val as number, y, z);
         }
 
         const parent = this._parent;