Ability to create and see discussion in a merge request
### Problem to solve
As a user, I want to see MR discussions inline when I open a file with discussions, so I can complete MRs more quickly.
### Proposal
When I checkout a branch that has an active MR and I open a file that has discussion items in that MR, the editor should show a decoration indicating a discussion on those lines. Clicking on the decoration should open an inset panel showing the discussion. In this way, it would behave like unstaged stages on a VCS tracked file.
### Further details
<!-- Include examples, use cases, benefits, goals, or any other details that will help us understand the problem better. -->
### Links / references
(description provided by @firelizzard)
<details>
<summary>Original issue description</summary>
It would be great for code reviewing if we could add comments directly from VS Code when browsing merge request.
</details>
issue