Consider opening source files in debugger as well

Currently we have our own source view but DevTools team suggested that we can also add an option open the devtools panel with the WebChannel. This option could possible be a context menu item. This way they can have more options and features.

There are some open questions though:
- Where do we open the debugger?
- new window? in a new tab? In an existing tab?
- How to attach to the right tab?
- Firefox-internal JS: Works only for live files, not files in another version of Firefox
- User files: How do we know if the website JS file is not changed?

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-777)