Allow other modules to alter the active link trail

Here is a patch for current module version 2.x

Having this feature definitely helps on top of the awesome work that this module does.
Tested patch in #9 and works as expected. Marking as RTBC.

fwiw, my use case was to parse menu items having links to view pages with contextual filters in the url path and add them to active trail - which became easy thanks to the hook!

Seems like the alter hook should maybe pass all possible patches so a module could pick one of those?

Also the service should gracefully handle when the injected service is not present, with an optional constructor argument and fall back to \Drupal::service() or people will have a fatal error that they might struggle to resolve.