Python Debugger should have a dependency on Python extension

[alexr00]

Testing #221

It looks like the Python Debugger extension can't be used without the Python extension. One way this could be solved is by making the Python Debugger have a dependency on the Python extension. Another option would be the have a better error here.

[MrZmcH]

@alexr00 Do I need to install the "ms-python" extension here? Is there anything else?

[alexr00]

Added to the April milestone so this gets verified.