feat: only allow bundled preload scripts (#17308)

docs/api/browser-window.md

@@ -266,6 +266,8 @@ It creates a new `BrowserWindow` with native properties as set by the `options`.
       When node integration is turned off, the preload script can reintroduce
       Node global symbols back to the global scope. See example
       [here](process.md#event-loaded).
+      **Note:** For security reasons, preload scripts can only be loaded from
+      a subpath of the [app path](app.md#appgetapppath).
     * `sandbox` Boolean (optional) - If set, this will sandbox the renderer
       associated with the window, making it compatible with the Chromium
       OS-level sandbox and disabling the Node.js engine. This is not the same as