AX: AXIsolatedTree::updateChildren sometimes fails to update isolated subtrees when...

https://bugs.webkit.org/show_bug.cgi?id=241735

Reviewed by Andres Gonzalez.

Our current algorithm in AXIsolatedTree::updateChildren is:

  1. If the object we got an AXChildrenChanged notification
  for is in the isolated tree, update its isolated children

  2. Otherwise, ascend the ancestry to the nearest
  in-isolated-tree ancestor, and update the children of that
  object

This is not always adequate when the object passed to updateChildren
is ignored, as in some cases the ancestor has no children changes
but the subtrees of the ignored object do.

This patch fixes this by also checking the live-children of the ignored
object for any that have unitialized children. If so, we call
AXIsolatedTree::updateChildren on those too.

* Source/WebCore/accessibility/AccessibilityObject.h:
(WebCore::AccessibilityObject::childrenInitialized const):
Move from private to public.
* Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.cpp:
(WebCore::AXIsolatedTree::updateChildren):

link: https://commits.webkit.org/251784@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@295779 268f45cc-cd09-0410-ab3c-d52691b4dbfc