fixup! Bug 30237: Add v3 onion services client authentication prompt

Fixes #41344 (closed) The fix is two-folds:

1. We cannot use about:blank as an interstitial while prompting, because it causes multiple navigation events which mess with the docShell ability to track the failed channel information; hence we switch to about:neterror, but styling it to fake about:blank appearance
2. We were notifying the content-side docShell that user cancelled the prompt using IPC messaging, but the listener was not registered in the correct process anymore because SessionStore has been moved in the parent process since last ESR; therefore now we directly load a short script in the proper docShell to make it display the error page.