16. 简化版 Ref 实现

简化版 Ref 实现，创建虚拟节点时获取 ref。

    export function createVnode(type, props, children?) {
      const shapeFlag = isString(type)
        ? ShapeFlags.ELEMENT // 元素
        : isObject(type)
        ? ShapeFlags.STATEFUL_COMPONENT // 组件
        : isFunction(type)
        ? ShapeFlags.FUNCTIONAL_COMPONENT
        : 0;
      const vnode = {
        __v_isVnode: true,
        type,
        props,
        children,
        key: props?.key,
        el: null,
        shapeFlag,
        ref: props && props.ref, // 提取ref
      };

function setRef(rawRef, vnode) {
	const refValue =
		vnode.shapeFlag & ShapeFlags.STATEFUL_COMPONENT
			? vnode.component.exposed || vnode.component!.proxy
			: vnode.el;

	if (rawRef) {
		rawRef.value = refValue;
	}
}
const patch = (n1, n2, container, anchor = null, parentComponent = null) => {
	// ...
	if (ref !== null) {
		// 新ref 和 老ref
		setRef(ref, n2);
	}
};