This route is declared by default in app/code/Magento/Ui/view/base/ui_component/etc/definition.xml:
<insertListing class="Magento\Ui\Component\Container">
<argument name="data" xsi:type="array">
<item name="config" xsi:type="array">
<item name="component" xsi:type="string">Magento_Ui/js/form/components/insert-listing</item>
<item name="update_url" xsi:type="url" path="mui/index/render"/>
<item name="render_url" xsi:type="url" path="mui/index/render"/>
<item name="autoRender" xsi:type="boolean">false</item>
<item name="dataLinks" xsi:type="array">
<item name="imports" xsi:type="boolean">true</item>
<item name="exports" xsi:type="boolean">false</item>
</item>
<item name="realTimeLink" xsi:type="boolean">true</item>
</item>
</argument>
</insertListing>
But in a listing ui_component XML it is also declared:
<argument name="data" xsi:type="array">
<item name="config" xsi:type="array">
<item name="component" xsi:type="string">Magento_Ui/js/grid/provider</item>
<item name="update_url" xsi:type="url" path="mui/index/render"/>
<item name="storageConfig" xsi:type="array">
<item name="indexField" xsi:type="string">page_id</item>
</item>
</item>
</argument>