<form>.reset() does not reset <selectedcontent>

[annevk]

What is the issue with the HTML Standard?

At least as far as I can tell, but there's web-platform-tests expecting this: https://github.com/web-platform-tests/wpt/blob/master/html/semantics/forms/the-select-element/customizable-select/selectedcontent.html

[josepharhar]

The reset algorithm for the select element calls the selectedness setting algorithm. Since this PR updates the selectedcontent element inside the selectedness setting algorithm, it should fix this issue as well: #11890