Proof of concept: Display the Content Editor for Markdown files in the Web IDE

What does this MR do and why?

It implements a proof of concept that illustrates a technical approach to use the Content Editor to edit Markdown files in the Web IDE and other areas of the GitLab application.

How does the feature work?

It displays the Content Editor when the active file is Markdown and the Web IDE is in Editor mode. Editor mode is different from review and commit modes.

Implementation notes

• We needed to implement a new API to track changes in the Content Editor to track when a file changes.
• I also had to remove the max-height constraints from the Content Editor CSS.

Screenshots or screen recordings

The following video gives a walkthrough this proof of concept

https://www.youtube.com/watch?v=bU9OGTWhjl0

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.