Update the preview image in 'Accessibility button & gesture' page.

* Put images in drawable/ and drawable-night/

Fix: 193081959
Fix: 193081959
Test: atest AccessibilityButtonPreviewPreferenceControllerTest
Change-Id: If0700e285920686cea6a815877af71fe6652d711

res/layout/accessibility_button_preview.xml

@@ -1,33 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!-- Copyright (C) 2021 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.
--->
-
-<FrameLayout
-    xmlns:android="http://schemas.android.com/apk/res/android"
-    android:layout_width="match_parent"
-    android:layout_height="wrap_content"
-    android:clipToPadding="false"
-    android:importantForAccessibility="noHideDescendants">
-
-    <ImageView
-        android:id="@+id/preview_image"
-        android:layout_width="match_parent"
-        android:layout_height="@dimen/accessibility_button_preview_height"
-        android:layout_gravity="center"
-        android:scaleType="fitCenter"
-        android:focusable="false"
-        android:clickable="false"
-        android:adjustViewBounds="true"/>
-</FrameLayout>