feat(widgets): stopwatch style picker and widget-picker previews

The stopwatch widget gets a per-instance style, chosen in a new
StopwatchConfigActivity on the APPWIDGET_CONFIGURE contract. Every widget
receiver now carries its own label, with a separate description, and the
widget picker shows sample-value preview layouts instead of a bare name.

app/src/main/AndroidManifest.xml

@@ -258,8 +258,19 @@
             </intent-filter>
         </activity>
 
+        <!-- The stopwatch widget's per-instance style picker: the same
+             APPWIDGET_CONFIGURE contract as the two above. -->
+        <activity
+            android:name=".ui.widget.config.StopwatchConfigActivity"
+            android:exported="true"
+            android:theme="@style/Theme.Clockula">
+            <intent-filter>
+                <action android:name="android.appwidget.action.APPWIDGET_CONFIGURE" />
+            </intent-filter>
+        </activity>
+
         <!-- The quick-timer widget's per-instance duration picker (M11): the
-             same APPWIDGET_CONFIGURE contract as the two above. -->
+             same APPWIDGET_CONFIGURE contract as the three above. -->
         <activity
             android:name=".ui.widget.config.QuickTimerConfigActivity"
             android:exported="true"
@@ -289,6 +300,7 @@
              change (widget/AnalogDateRefresh.kt). -->
         <receiver
             android:name=".widget.NextAlarmWidgetReceiver"
+            android:label="@string/widget_next_alarm_label"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
@@ -300,6 +312,7 @@
 
         <receiver
             android:name=".widget.TimerWidgetReceiver"
+            android:label="@string/widget_timer_label"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
@@ -311,6 +324,7 @@
 
         <receiver
             android:name=".widget.ClockWidgetReceiver"
+            android:label="@string/widget_clock_label"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
@@ -322,6 +336,7 @@
 
         <receiver
             android:name=".widget.AnalogClockWidgetReceiver"
+            android:label="@string/widget_analog_label"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
@@ -333,6 +348,7 @@
 
         <receiver
             android:name=".widget.StopwatchWidgetReceiver"
+            android:label="@string/widget_stopwatch_label"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
@@ -344,6 +360,7 @@
 
         <receiver
             android:name=".widget.QuickTimerWidgetReceiver"
+            android:label="@string/widget_quick_timer_label"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />