R1:dbc72a05bc39

Correct the behavior of "Desktop Only" in Notifications preferences

Summary:
See <https://discourse.phabricator-community.org/t/desktop-only-notifications-mode-is-broken/1234>. Ref T13102. The "Desktop Only" mode for notifications currently shows both desktop and web notifications.

In fact, `JX.Notification` currently has no ability to render notifications as desktop-only. Make this work.

Note that many of the variables and parameters here, including `showAnyNotification`, `web_ready`, and…