createW3CTreeStrategy

Description#

Default W3C APG treeview keyboard policy:

• ArrowRight on a collapsed parent expands it. On an already-open parent it moves the active-descendant to the first child. On a leaf it is a no-op.
• ArrowLeft on an open node collapses it. On a closed node (or leaf) with a parent it moves the active-descendant to the parent. On a root leaf it is a no-op.

Move actions internally verify that ad.highlightByValue actually changed activeId (e.g. disabled skip rejection), and downgrade to 'noop' when it didn't - so consumers bound to (movedToChild) / (movedToParent) only see state-change-truthful emissions.