Bug 1787282: [Part 2] Cache LINKS_TO relation information r=Jamie

Differential Revision: https://phabricator.services.mozilla.com/D156138

accessible/base/CacheConstants.h

@@ -81,6 +81,7 @@ static constexpr RelationData kRelationTypeAtoms[] = {
      Some(RelationType::DESCRIPTION_FOR)},
     {nsGkAtoms::aria_flowto, nullptr, RelationType::FLOWS_TO,
      Some(RelationType::FLOWS_FROM)},
+    {nsGkAtoms::link, nullptr, RelationType::LINKS_TO, Nothing()},
 };
 
 }  // namespace a11y