Feature request: Show as margin instead of toolwindow

[sboulema]

Show as margin instead of toolwindow.

Split from: #167

Links

https://github.com/microsoft/VSExtensibility/tree/main/New_Extensibility_Model/Samples/WordCountMargin

[sboulema]

First (naive) implementation:

Couple of issues:

• Width of the margin is not adjustable
• Line selection highlight runs through the margin