Validate people's settings

[brettcannon]

If you look at some of the issues that people file, e.g. #418, they stem from mis-configuration. Some of the common issues are:

• CLI args where the space is embedded in a string instead of as two separate items, e.g. ["--hello world"] instead of ["--hello", "world"]
• Invalid/ambiguous python.pythonPath
• Invalid PYTHONPATH values
• Ensure users do not select the executable pythonw.exe instead of python.exe

[brettcannon]

When someone has a .env folder without specifying a specific envvar file location (and if we don't emit parse errors for the .env file, that too 😉 ). Seems like people like naming their virtual environments .env and don't know that is a common default file name.

[DonJayamanne]

However that (file or folder name) shouldn't cause any problems (not anymore).

[luabud]

This may be related: https://code.visualstudio.com/updates/v1_38#_validation-for-string-array-settings

[brettcannon]

Closing this as being too broad of an idea; should be tackled on a setting-by-setting situation.