Whether the semantics node label is the name of a visually distinct route.
This is used by certain widgets like Drawers and Dialogs, to indicate that the node's semantic label can be used to announce an edge triggered semantics update.
Semantic nodes annotated with this flag will still receive a11y focus.
Updating this label within the same active route subtree will not cause additional announcements.
static const SemanticsFlag namesRoute = SemanticsFlag._(_kNamesRouteIndex)