refactor(ReaderMode): consider using iframe instead of dialog

[maxpatiiuk]

Consider displaying the reader mode using iframe instead of dialog
While the dialog is easy to use, it does not provide sufficient isolation from styles, scroll jacking, keyboard intercept, CSS filters, and the rest, even inside the Shadow DOM

i.e https://chromewebstore.google.com/detail/dom-distiller-reading-mod/oiembdaoobijmdmeobkalaehgifealpl works that way

However there are also cons of doing that:

• Iframe would work worse with other tools, extensions, and screen readers. It might work worse with printing too
  • i.e dom distiller extension has some people complaining that the extension doesn't play nicely with other extensions