Previously, the router would merge path and matrix params, as well as
data/resolve, with special rules (only merging down when the route has
an empty path, or is component-less). This change adds an extra option
"paramsInheritanceStrategy" which, when set to 'always', makes child
routes unconditionally inherit params from parent routes.
Closes#20572.
* The problem was with the `fireChildActivationStart` function. It was taking a `path` param, which was an
array of `ActivatedRouteSnapshot`s. The function was being fired for each piece of the route that was being
activated. This resulted in far too many `ChildActivationStart` events being fired, and being fired on routes
that weren't actually getting activated. This change fires the event only for those routes that are actually
being activated.
fixes#18942
PR Close#19043
* Introduced with #18407, `RouteEvents` don't actually have a common constructor. Reverting here to be able to add new functionality to ChildActivation events.
PR Close#19043
