Add theme to widget mask to have light/dark mode

Without the theme, the colors do not change when in dark mode.

Fix: 187907544
Test: Put a WP widget, turn off WP, turn dark mode on/off
Change-Id: I682ea35667abe7f584788e06495bd2968ce45b34

core/res/res/layout/work_widget_mask_view.xml

@@ -15,6 +15,7 @@ Copyright (C) 2015 The Android Open Source Project
     limitations under the License.
 -->
 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:theme="@android:style/Theme.DeviceDefault.DayNight"
     android:id="@android:id/background"
     android:layout_width="match_parent"
     android:layout_height="match_parent"