This feature is now available in Visual Studio 2019 version 16.3.0 (release notes).
- You can use the
<i>or<em>tags for italic. - You can use the
<b>or<strong>tags for bold. - From the release notes, a variety of html tags seem to be supported, but the official documentation doesn’t seem to be updated with this new feature just yet.
It looks like this: 
.