overlay: enable productivity_device for DocumentsUI

<?xml version="1.0" encoding="utf-8"?>

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     Licensed under the Apache License, Version 2.0 (the "License");

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<resources>

    <!-- Flags setup as productivity oriented in which case Downloads app will be presented

             as Files app. Including showing of the Documents and "advanced" roots. -->

    <bool name="productivity_device">true</bool>

</resources>