AX: WebKit should expose reciprocal AXLinkedUIElement relationships between a selected tab and its expanded tabpanel
In ARIA tab patterns, a selected tab should reference the IDREF of its selected tabpanel using @aria-controls. WebKit should expose this as AXLinkedUIElement, so that VoiceOver users can jump to the tab contents with VO+J. Likewise, the reciprocal relationship should be exposed from a tabpanel back to its controlling tab. VO+J would then cycle back and forth between the related tabs and their panels.