Javascript console for Web IDE client evaluation

Extending the Web IDE client evaluation live preview https://gitlab.com/gitlab-org/gitlab-ce/issues/47268 we should add a Javascript console for debugging and testing. This will mean that a user doesn't need to open a web inspector manually for the iframe

Proposal

Add the ability for the user to also open a Javascript console for debugging the live preview, testing functions etc.

Links / references

• Live preview https://gitlab.com/gitlab-org/gitlab-ce/issues/47268
• Design discovery https://gitlab.com/gitlab-org/gitlab-ce/issues/47887