Show an agenda in the clock widget's dynamic zone, with multiple slots

The dynamic zone showed exactly one part: the highest ranked of the enabled
ones. It now shows up to `clockWidgetDynamicZoneSlots` of them (default 1),
adjustable with a slider in the clock widget settings whose maximum is the
number of enabled parts. `ClockWidgetVM.getActiveParts()` returns that sorted
list, and both clock layouts render it (stacked under the clock, or next to it
in the horizontal layout).

On top of that the zone has an "Events" part (`clockWidgetCalendarPart`, off by
default) that shows today's agenda: events that are still running or upcoming
today, plus today's all-day events. At most four rows; when there are more, the
last row is a "+N more events" hint that opens the calendar app. Tapping a row
opens the event through `CalendarEvent.launch()`.

A row is three fixed-width columns that are pure layout, not drawn: a dot in the
calendar's colour, the time, and the title (ellipsized when it does not fit).
Times are always times, never dates - an all-day event renders "all-day" - and
the block is centred under the clock. The columns line up across rows, and the
time is left-aligned within its column.

The part ranks 70 when an event is running or starts within half an hour, 30
while events are left today and 0 on an empty day, so the date keeps the slot
when there is nothing to show. It reloads itself through a ContentObserver on
CalendarContract.Events and a 15 minute ticker, because unlike the calendar
widget it is on screen all the time. Tasks (`CalendarEvent.isTask`) are filtered
out for now; a tasks part can reuse this once tasks are configured.

Verified on the Titan 2: with the part enabled and three slots, the home screen
shows the agenda (two all-day events and a timed one) above the date part.

core/i18n/src/main/res/values/strings.xml

@@ -598,6 +598,7 @@
     <string name="preference_clock_widget_alignment_center">Center</string>
     <string name="preference_clock_widget_alignment_bottom">Bottom</string>
     <string name="preference_clockwidget_dynamic_zone">Dynamic zone</string>
+    <string name="preference_clockwidget_dynamic_zone_slots">Visible parts</string>
     <string name="preference_clockwidget_smartspacer">Managed by Smartspacer</string>
     <string name="preference_clockwidget_date_part">Date</string>
     <string name="preference_clockwidget_date_part_summary">Show the current date</string>
@@ -612,6 +613,13 @@
     <string name="preference_clockwidget_battery_part_hide">Off</string>
     <string name="preference_clockwidget_alarm_part">Alarms</string>
     <string name="preference_clockwidget_alarm_part_summary">Show alarms that will ring within the next 8 hours</string>
+    <string name="preference_clockwidget_calendar_part">Events</string>
+    <string name="preference_clockwidget_calendar_part_summary">Show today\'s agenda</string>
+    <string name="clockwidget_calendar_part_all_day">all-day</string>
+    <plurals name="clockwidget_calendar_part_more_events">
+        <item quantity="one">+%d more event</item>
+        <item quantity="other">+%d more events</item>
+    </plurals>
     <string name="preference_screen_backup">Backup and restore</string>
     <string name="preference_screen_backup_summary">Export and import launcher data</string>
     <string name="preference_backup">Backup</string>