Hover doesn't render sub/sup html elements in Markdown text

[fbricon]

Hover doesn't render sub/sup html elements in Markdown text.

• VSCode Version: 1.9.1/1.10.0-insider
• OS Version: macOS 10.12.3

Steps to Reproduce:

1. hover over some text returning x<sup>x+1</sup>. x<sub>i+1</sub>
2. Text should be rendered as x^x+1. x_i+1

This follows up on redhat-developer/vscode-java#155, where I'm now trying to make Javadoc return sub/sub HTML tags as-is, in the Markdown text (unreleased WIP):

The Markdown rendering engine in VS Code supports it, as can be seen in the Markdown preview pane, just not in hover mode.

[jrieken]

The MarkedString is strictly markdown without embedded html or scripts. Closing as dupe of #11877. The idea is to allow Html (w/o scripts and styles) in addition to Markdown. I think that would suite javadoc well because it often html-elements frequently