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