Formatting UX is weird in DCR discussion

[From Paolo Castro](https://groups.google.com/a/guardian.co.uk/g/dotcom.platform/c/GkGg53fY-OQ/m/cyo-KUSjBQAJ):

> When I press two markdowns in a row, the closing tag for the second markdown places itself inside the text that was highlighted ([video](https://drive.google.com/file/d/14cY0muwAhZdEAbuInQEhC2zmtm9gZziW/view?usp=sharing))

> It means that readers who want to add two formats to text will need to highlight the text, select the format, highlight the text again, and then select the next format. It would be great if it remembered the whole text and inserted the closing tag properly.