Support Namespace Packages In Python Code Intelligence

[ggilmore]

Our python language server's data model doesn't support namespace packages very well.

Supporting this properly would require a rather large refactor of the existing logic.

[sqs]

The MS Python lang server (which is probably what we will switch to using) does not seem to support namespace packages either:

• Python Language Server doesn't seem to work with namespace packages microsoft/python-language-server#71
• New Python Language Server doesn't seem to work with namespace packages microsoft/vscode-python#2527