Swap point for how a routed tab set decides which tab the URL belongs
to. Default createTabUrlMatch.
Override when neither shipped policy fits: locale-segment-insensitive
comparison (/de/rounds and /en/rounds are the same tab), matching
on a route data key instead of the path, or a permission-aware read
that skips tabs the user cannot open. routeFor only changes what a
tab's route is; this changes how it is compared.
Mirrors CNGX_TABS_COMMIT_ACTION on the write side: the
navigation a tab switch performs is already swappable, so the read that
mirrors navigation back onto activeIndex should be too.