Adopt `@vscode/python-extension` to fetch Python extension API in all extensions which use the template

[karrtikr]

We now have a npm package which carries the Python extension api types, which makes it easier to track changed api types and also has a helper function which can be used to access the API:

Instructions to adopt can be found here: https://github.com/microsoft/vscode-python/blob/main/pythonExtensionApi/README.md