Update inteliJ plugin to support latest GoRouter version

[DavidDWiser]

With the release of a new version of go_router_builder the structure of generated routes has changed. Now each route mixes in a mixin that follows the pattern _$RouteName, where the RouteName is the name of the actual route.

This means that a route that previously looked like this:

class LoginRoute extends GoRouteData implements RouteDataModel {
 /// ...
}

when generated will look like this:

class LoginRoute extends GoRouteData 
  with _$LoginRoute
  implements RouteDataModel {
 /// ...
}

Because of that, the inteliJ plugin needs to be updated to support latest GoRouter version.

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Dev note: Due to the way Dart works, mixins (declared with the with keyword) need to be specified before any interfaces (declared with the implements keyword).