Super sidebar accessible landmark element

Follow-up from discussion in Super sidebar accessibility review (#394793 - closed) • Scott de Jonge • 16.0

Currently the super sidebar container element is <aside> which has a complementary role.

<section> may be more appropriate than <aside> (or <div> with role="region" and aria-label) as <aside> meant for content that is complimentary to the <main> page content.