I'm attempting to use a 3rd party (Mapbox) basemap in 4.3 JavaScript API. I need to include copyright and links in the map attribution as per Mapbox's policy. I've included the html as a string in the layers copyright property, but the string is not 'translated' into html and instead shows the html as text.
<SPAN class="keyword token">var</SPAN> basemap <SPAN class="operator token">=</SPAN> <SPAN class="keyword token">new</SPAN> <SPAN class="token class-name">WebTileLayer</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">{</SPAN>
urlTemplate<SPAN class="punctuation token">:</SPAN> <SPAN class="string token">"..."</SPAN><SPAN class="punctuation token">,</SPAN>
copyright<SPAN class="punctuation token">:</SPAN> <SPAN class="string token"><SPAN>'© <a href="</SPAN><A class="jive-link-external-small" href="https://community.esri.com/external-link.jspa?url=http%3A%2F%2Fwww.openstreetmap.org%2Fcopyright" target="_blank">http://www.openstreetmap.org/copyright</A><SPAN>">OpenStreetMap</a> contributors, © <a href="</SPAN><A class="jive-link-external-small" href="https://community.esri.com/external-link.jspa?url=https%3A%2F%2Fwww.mapbox.com%2Fmap-feedback%2F" target="_blank">https://www.mapbox.com/map-feedback/</A><SPAN>">Mapbox</a>'</SPAN></SPAN>
<SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
map<SPAN class="punctuation token">.</SPAN><SPAN class="token function">add</SPAN><SPAN class="punctuation token">(</SPAN>basemap<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN><SPAN class="line-numbers-rows"><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN></SPAN>Output:

The behavior can also be seen in this sample (click the attribution to see the Stamen copyright shown as text): ArcGIS API for JavaScript Sandbox
This was valid in the 3.x API, how do I do this at 4.x?