accessDialog: Skip focus check for screenshot permissions
Screenshot is a special case compared to other permissions because apps might want to hide themselves from the desktop when a screenshot is about to be taken. In that case, this heuristic of checking if the focus window corresponds to the application that is requesting screenshot permissions becomes problematic.
Special case the screenshot permission to skip the focused window check.
See also: https://github.com/flatpak/xdg-desktop-portal/pull/851