Default implementations of javaScriptAlert/Confirm/Prompt treat message as rich text

When e.g. running alert("<h1>foo</h1>") (and same with confirm() and prompt()) in the simplebrowser devtools, the message window shows formatted text.

Compare this with Chromium, where the text is output as-is, as JavaScript dialogs shouldn't be able to show HTML as part of the browser UI.

It could be argued that this is a (small) security vulnerability, since it could be used for phishing purposes with some elaborate text (think faking an "update available" dialog from a web browser with a link to some malware).

This happens because in src/webenginewidgets/api/qwebenginepage.cpp, QWebEnginePage::javaScriptAlert uses QMessageBox::information() which uses Qt::RichText as text format by default (and javaScriptConfirm / javaScriptPrompt do something similar).