Add settings for scheduling dark theme

Adding a settings page similar to night light for Dark theme. it will allow the user to schedule
dark mode from sunrise to sunset

Test: make -j64 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.display.DarkUIPreferenceControllerTest" && \
make -j64 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.display.darkmode.DarkModeActivationPreferenceControllerTest" && \
make -j64 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.display.darkmode.DarkModeObserverTest" && \
make -j64 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.display.darkmode.DarkModeScheduleSelectorControllerTest"

Fixes: 141567787

Change-Id: I3094b655c04f59c23a95162a1be5ee8260e28a48

res/layout/dark_ui_activation_button.xml

@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Copyright (C) 2019 The Android Open Source Project
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+  -->
+
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:minHeight="?android:attr/listPreferredItemHeight">
+
+    <Button
+        android:id="@+id/dark_ui_turn_on_button"
+        style="@style/ActionPrimaryButton"
+        android:layout_marginStart="@dimen/screen_margin_sides"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center_vertical" />
+
+    <Button
+        android:id="@+id/dark_ui_turn_off_button"
+        style="@style/ActionSecondaryButton"
+        android:layout_marginStart="@dimen/screen_margin_sides"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center_vertical" />
+
+</LinearLayout>