Handle empty attribute values in SearchListItem

[camdendotlol]

Summary

This PR updates SearchListItem to handle situations when one or more attribute values are empty.

• when all values are empty, do not display the <ul> at all
• when a given value is empty, don't render its <li> element or icon

As a byproduct of these changes I've moved attribute values into a memoized array, which should give some performance improvements as we're no longer calling every attribute's render callback on every render.