Accessibility shortcut secondary action - improve shortcutPreference

1. Use setWidgetLayoutResource() for the controllable widget at the
right side.
2. Improve listener structure.
3. Extend checkbox clickable area.

Bug: 142530063
Test: make -j52 RunSettingsRoboTests ROBOTEST_FILTER=ShortcutPreferenceTest
Change-Id: Iebb9f62653914a0d7200c627f01cf7953d576960
diff --git a/res/layout/preference_widget_settings.xml b/res/layout/preference_widget_settings.xml
new file mode 100644
index 0000000..73c6875
--- /dev/null
+++ b/res/layout/preference_widget_settings.xml
@@ -0,0 +1,27 @@
+<?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
+  -->
+
+<!-- Layout used by ShortcutPreference. This is inflated inside android.R.layout.preference. -->
+<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/settings_button"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:layout_gravity="center"
+    android:background="?android:attr/selectableItemBackground"
+    android:scaleType="center"
+    android:src="@drawable/ic_mode_edit"
+    android:contentDescription="@string/settings_button" />