Views tabs missing contextual links on AJAX-loaded tabs

Problem/Motivation

Views-based tabs loaded via AJAX are missing contextual links (the "edit view" pencil). The initial/default tab renders them correctly because its View render array passes through the normal render pipeline where contextual_preprocess() picks up #contextual_links.

AJAX-loaded tabs don't get contextual links because ViewContent::doRender() eagerly renders the View with renderRoot() and returns #markup. By the time the render array reaches the template layer, it's flat HTML and contextual_preprocess() never sees the #contextual_links.

Steps to reproduce

1. Create a QuickTabs instance with AJAX enabled and multiple Views tabs.
2. View the page as a user with "access contextual links" permission.
3. The default tab shows the contextual links pencil.
4. Click a secondary tab. No contextual links appear.

Proposed resolution

Add #contextual_links to the View's render array inside ViewContent::doRender(), after $view->buildRenderable() but before the renderRoot() call. This way they're part of the render array when it gets processed and survive the eager rendering on the AJAX path.