Restart Kernel for C# notebooks

[marckruzik]

Is your feature request related to a problem? Please describe.
I'm working with C# notebooks (ipynb), and there are cases where I need to restart the C# Kernel.

Describe the solution you'd like
When working with Python I can restart the Python Kernel.
So when I am working with C#, I would like to be able to restart the C# Kernel.

Describe alternatives you've considered
Currently, I have to close and reopen VS Code each time I want to restart the C# Kernel.

[marckruzik]

I found by chance that there is a command to restart the current notebook's kernel.

So the enhancement proposal would become the following:
Add a button to use the command "restart the current notebook's kernel".
This button should be the same than the one we have when working with Python interactive:

[claudiaregio]

I think we should add this to achieve toolbar parity with Python, I don't think core will tackle the shared icon for a while.

[marckruzik]

Fixed by #2326.