Use dav SEARCH for better results

See nextcloud/server#14313

await axios({
  method: 'SEARCH',
  url: '/remote.php/dav/',
  headers: {'requesttoken': OC.requestToken, 'content-Type': 'text/xml'},
  data: `<?xml version="1.0" encoding="UTF-8"?>
<d:searchrequest xmlns:d="DAV:" xmlns:oc="http://owncloud.org/ns">
    <d:basicsearch>
        <d:select>
            <d:prop>
                 <oc:fileid/>
                 <d:displayname/>
                 <d:getcontenttype/>
                 <d:getetag/>
                 <oc:size/>
            </d:prop>
        </d:select>
        <d:from>
            <d:scope>
                <d:href>/files/admin/</d:href>
                <d:depth>infinity</d:depth>
            </d:scope>
        </d:from>
        <d:where>
            <d:like>
                <d:prop>
                    <d:getcontenttype/>
                </d:prop>
                <d:literal>image/%</d:literal>
            </d:like>
        </d:where>
        <d:orderby>
            <d:prop>
                <oc:size/>
            </d:prop>
            <d:ascending/>
        </d:orderby>
    </d:basicsearch>
</d:searchrequest>`
});

Start with the axios DAV SEARCH example in this issue and read the linked nextcloud/server#14313 discussion for context. Then locate the viewer's search entry point and compare its current request with the example; done means the viewer uses DAV SEARCH and produces better search results.