Fix up Python extension recommendations

[SaschaCowley]

Currently, our extensions.json lists both ms-python.python and ms-python.vscode-pylance, despite the fact that the Python extension installs Pylance by default. Since the extension works best with the Python Debugger extension installed, we should either:

1. Remove the explicit recommendation of Pylance, and just rely on the other extensions recommended by the Python extension; or
2. Add Python Debugger to the recommendations to make our recommendation explicit.

[seanbudd]

Is the python debugger extension useful/accessible?

[michaelDCurran]

Is the python debugger extension useful/accessible?
Absolutely. It is required to run debug sessions in VS Code for Python projects, including break points, call stacks, watching variables, runtime execution of Python code within the debugged process.

[SaschaCowley]

As Mick has said, yes. Additionally it's required (if you want to debug Python) for the remote debugging method I'm writing up. I can open a PR to include everything required for that method (launch.json and changes to extensions.json) all at once if that's preferable.