Preserve query string in redirect

The issue still exists in 3.x branch and it is an issue if you are using Oauth authentication.

Steps to reproduce:

* Add a required agreement to your site
* Bind your site to a Oauth login flow
* When you get a call to /oauth2/authorize the Agreement module catches the request and redirects the user to the agreement form (which is a good thing)
* (Read and) agree to the Agreement, submit the form
* Your authentication is broken since the extra arguments injected in the call to /oauth2/authorize have been trimmed.

We need to preserve the query parameters to let the user login properly after agreeing to the Agreement (and reading it!).

As a side effect of trying to switchover to GitLab CI, I've needed to refactor the subscriber, so I've been working on this in 🐛 Refactor event subscriber to use LocalRedirectResponse to fix GitLab CI Active .

I added a functional test for this as well.

Unfortunately I needed to go in a different direction. I'll keep this open until 🐛 Refactor event subscriber to use LocalRedirectResponse to fix GitLab CI Active is merged/resolved.

Resolved in 3.0.x-dev

Automatically closed - issue fixed for 2 weeks with no activity.