Bug 1821156: Map hgroup element to group role, r=Jamie

Per HTML AAM, HTML hgroup elements should have an implicit role=group instead
of being generics. This revision implements that by mapping hgroup elements to
roles::GROUPING in HTMLMarkupMap. It also removes the expected fail from the
relevant web platform test, which we now pass.

Differential Revision: https://phabricator.services.mozilla.com/D200204

Author: Nathan LaPre

accessible/base/HTMLMarkupMap.h

@@ -207,6 +207,8 @@ MARKUPMAP(h5, New_HyperText, roles::HEADING)
 
 MARKUPMAP(h6, New_HyperText, roles::HEADING)
 
+MARKUPMAP(hgroup, New_HyperText, roles::GROUPING)
+
 MARKUPMAP(
     hr,
     [](Element* aElement, LocalAccessible* aContext) -> LocalAccessible* {

testing/web-platform/meta/html-aam/roles.html.ini

@@ -14,9 +14,6 @@
   [el-dfn]
     expected: FAIL
 
-  [el-hgroup]
-    expected: FAIL
-
   [el-dd]
     bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1829028
     expected: FAIL