[Task link](https://www.pivotaltracker.com/story/show/184012434)
This PR implements Intermediate Representation for our documentation. Later these data structures would be used to generate HTML and CSS for the documentation panel. For now, we display it in the debug scene.
https://user-images.githubusercontent.com/6566674/210674850-480a3e6e-76c3-4f34-a235-15c44dc9ec01.mp4
# Important Notes
- `suggestion-database` now lives in a separate crate
- also, two utility crates were introduced for the `notification` and `executor` modules of enso-gui
- documentation debug scene is moved to a separate crate
- All refactorings are done in the last two commits
The old JS-based Welcome Screen was removed and replaced with the Rusty one.
Co-authored-by: Adam Obuchowicz <adam.obuchowicz@enso.org>
Co-authored-by: Adam Obuchowicz <adam.obuchowicz@luna-lang.org>
