Proof of concept for the components that will render the top bar

Hello!
We have that POC in https://www.drupal.org/project/drupal/issues/3401826#comment-15837369 🌱 [PLAN] Top contextual bar Active

@finnsky if you think the code is still useful could you please move it to this issue?

Top Bar has moved along quite a bit since this issue was raised. We are past Top Bar POC stage. This issue is no longer relevant. Closing as outdated.