Add privapp-permissions for DocumentsUI

DocumentsUI use @hide private permission:
    "android.permission.CHANGE_OVERLAY_PACKAGES"

Test: atest DocumentsUITests
Test: check CHANGE_OVERLAY_PACKAGES grant to DocumentsUI.apk
Test: check CHANGE_OVERLAY_PACKAGES grant to com.android.documentsui
Test: com.android.documentsui.xml locate in system/etc/permissions
Test: DocumentsUI.apk locate in /system/priv-app/

Bug: 128689309
Bug: 131331107
Bug: 132671058

Change-Id: Ie9bffbe152da511dc08882fd44e95dd426aef980

data/etc/Android.bp

@@ -73,6 +73,13 @@ prebuilt_etc {
     filename_from_src: true,
 }
 
+prebuilt_etc {
+    name: "privapp_whitelist_com.android.documentsui",
+    sub_dir: "permissions",
+    src: "com.android.documentsui.xml",
+    filename_from_src: true,
+}
+
 prebuilt_etc {
     name: "privapp_whitelist_com.android.launcher3",
     product_specific: true,

data/etc/com.android.documentsui.xml

@@ -0,0 +1,21 @@
+<?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
+  -->
+<permissions>
+    <privapp-permissions package="com.android.documentsui">
+        <permission name="android.permission.CHANGE_OVERLAY_PACKAGES"/>
+    </privapp-permissions>
+</permissions>