**Why?**
- This is needed for the Web Terminal feature.
  https://gitlab.com/gitlab-org/gitlab-ee/issues/5426

**Notes:**
- Introduces a `pane` Vuex module.
- Some views should not be kept alive (i.e. job details).
  This is why a `keepAlive` flag was introduced for views.

This enables JavaScripts projects to have live previews straight in the
browser without requiring any local configuration. This uses the
CodeSandbox package `sandpack` to compile it all inside of an iframe.

This feature is off by default and can be toggled on in the admin
settings. Only projects with a `package.json` and a `main` key are
supported.

Updates happen in real-time with hot-reloading. We just watch for
changes to files and then send them to `sandpack` to allow it to reload
the iframe. The iframe includes a very simple navigation bar, the text
bar is `readonly` to stop users navigating away from the preview and
the back and forward buttons just pop/splice the navigation stack
which is tracked by a listener on `sandpack`

There is a button inside the iframe which allows the user to open the
projects inside of CodeSandbox. This button is only visible on
**public** projects. On private or internal projects this button
get hidden to protect private code being leaked into an external
public URL.

Closes #47268