No scroll after show hover (`gh`)

Describe the bug
Press 'gh' when the cursor is on a function call. There is no way to see the content of a docstring when it doesn't fit in the hover box that appears. That is, scrolling in the hover box is impossible.

Contrast this to when you hover with the mouse. In this case you can use the scroll wheel to inspect the entire docstring.

This seems to be related to the comment by @unode in https://github.com/VSCodeVim/Vim/issues/1703#issuecomment-461607742 .

To Reproduce
Steps to reproduce the behavior:

1. Go to a function call that has a substantial docstring.
2. type 'gh'
3. see that you cannot view the entire docstring and cannot scroll
4. move the mouse to the hover box and see that it disappears

Expected behavior
I expect to have a key (or combination) that will scroll the hover box. The combination 'gh' is rather useless without this functionality.

Screenshots

Environment (please complete the following information):

• Extension (VsCodeVim) version: v1.7.1
• VSCode version: 1.33.1
• OS: Linux (Ubuntu)

Additional context
Add any other context about the problem here.

Reproduce the issue in VSCodeVim by placing the cursor on a function call with a long docstring and invoking gh, then compare it with mouse-triggered hover behavior. Trace the gh keybinding and hover interaction entry points; done means the keyboard-triggered hover can be inspected beyond the visible area without disappearing.