Decline option in pull requests should allow formatted text (BB-10955)

I can add fully formatted, Markdown-based text, as comment to any pull request, but I can't do this in decline reason window. Anything I enter there is not formatted, new-lines are stripped and in the result, decline reason (if longer than usual) ends up as nearly-unreadable long one-line string. Why?

This should be fixed. If we use formatted text nearly everywhere, we should use it for reasons and other texts as well.