feat(ring): optionally open the ring screen over other apps

A full-screen intent is only a heads-up on a phone in use. A new, opt-in
setting under Alarms lets a ringing alarm or timer open its screen over
the app in use instead. It relies on "display over other apps", which
turning the setting on sends the user to grant; the switch reads as off
while the permission is missing. A locked or dark phone is still left
to the full-screen intent, so the screen never opens twice.

app/src/main/res/values/strings.xml

@@ -344,6 +344,8 @@
     <!-- #18: what the volume buttons do while an alarm rings -->
     <string name="settings_volume_buttons">Volume buttons while ringing</string>
     <string name="settings_volume_buttons_hint">Applies to every alarm while its ring screen is showing. With a dismiss challenge set, Dismiss snoozes instead, so the challenge still has to be done. When a snooze is called for but none are left, the buttons change the volume instead and the alarm keeps ringing.</string>
+    <string name="settings_ring_over_other_apps">Ring screen over other apps</string>
+    <string name="settings_ring_over_other_apps_hint">When an alarm or timer goes off while you\'re using another app, show its ring screen instead of a notification. Needs permission to display over other apps.</string>
     <string name="volume_buttons_control_volume">Change the volume</string>
     <string name="volume_buttons_snooze">Snooze</string>
     <string name="volume_buttons_dismiss">Dismiss</string>