Improve "No Python interpreter" selected prompt

[roblourens]

Environment data

• VS Code version: 1.62-insider
• Extension version (available under the Extensions sidebar): v2021.10.1317843341

I think this just showed up today, but I can't give exact repro steps. I was doing python things in different repos for awhile. At some point, I noticed that I get this notification every time I open a window with a python project

I don't usually see that. Then I noticed that I have this setting, which I definitely didn't set manually: "python.defaultInterpreterPath": "/opt/python/latest/bin/python". Removing that makes the notification go away. Is there something in the extension that adds that setting? That path does not exist for me.

[karrtikr]

Then I noticed that I have this setting, which I definitely didn't set manually:

We set it in User settings when an interpreter is chosen manually, but we never modify this setting for the workspace as far as I'm aware of.

Instead of "No Python Interpreter is selected" prompt, we should show a "Invalid Python Interpreter selected" prompt, we'll fix that with this issue.