The current implementation for redirecting users inside guards was in place
before the feature was added to allow `CanActivate` and `CanActivateChild` guards
to return `UrlTree` for redirecting users.
Returning `UrlTree` should be the default method, as it provides a more desirable
redirecting experience. When using `router.navigate` followed by `return false`,
the `Router` calls `resetUrlToCurrentUrlTree` (in the `finalize` operator) before
processing the navigation to the new route. This can result in an undesirable
history if the navigation was the first navigation in the application - that is,
the route will briefly be reset to just `/` (see #36187).
Fixes#36187
PR Close#37100
Previously, the example in the `router` guide was not
preserving the query params after logging in.
This commit fixes this by using `navigate` instead of
using `navigateByUrl`, which ignores any properties in
the `NavigationExtras` that would change the provided URL.
Fixes 34917
PR Close#35176
