src/vs/workbench/services/actions/common/menusExtensionPoint.ts/isValidItems
	export function isValidItems(items: (IUserFriendlyMenuItem | IUserFriendlySubmenuItem)[], collector: ExtensionMessageCollector): boolean {
		if (!Array.isArray(items)) {
			collector.error(localize('requirearray', "submenu items must be an array"));
			return false;
		}

		for (let item of items) {
			if (isMenuItem(item)) {
				if (!isValidMenuItem(item, collector)) {
					return false;
				}
			} else {
				if (!isValidSubmenuItem(item, collector)) {
					return false;
				}
			}
		}

		return true;
	}