When the runtime is reloaded in-process (NativeScriptRuntime.reloadApplication,
used for OTA soft reboots) the app re-runs main in a fresh JS isolate while the
process stays alive. iOSApplication.run() sees a live UIApplication and routes
to runAsEmbeddedApp()

- The previous UIWindow was deallocated along with the old isolate (it was
  retained only by the JS-side SceneDelegate._window), and
  sceneWillConnectToSession — which creates the window — does not re-fire on a
  reload. getWindow() then returned null and runAsEmbeddedApp() bailed early,
  leaving a black screen.
- With no embedder delegate (NativeScript owns the UIApplication), the new root
  was presented modally over the old, now-dead root controller instead of
  replacing it — leaking the old controller on every reload and breaking when an
  overlay is mid-presentation.

runAsEmbeddedApp() now:
- recreates a window bound to the active UIWindowScene when none is found
  (initWithWindowScene + _setWindowForScene/_setupWindowForScene);
- moves the rootViewController guard into the embedder-only branch, since a
  freshly recreated window has no controller yet;
- replaces the window root via setWindowRootView() for the NativeScript-owned
  case instead of modal-presenting over the stale root.

Co-authored-by: Nathan Walker <walkerrunpdx@gmail.com>