New workspace virtual environments are not discovered until VS Code reloads

[qubitron]

Environment data

VS Code version: 1.19.3
Python Extension version: 2018.1 Beta
Python Version: Python 3.6
OS and version: Windows 10

Actual behavior

New virtual environments in your workspace root are not shown in the Select Interpreter list until restarting VS code

Expected behavior

New virtual environments within the workspace are shown upon running select interpreter

Steps to reproduce:

• Created a new virtual environment from the terminal at the workspace root
• Select interpreter from VS Code

[brettcannon]

We are going to scope this to just virtual environments created in the workspace folder (should take into consideration the fact that pipenv can create its virtual environment locally when a certain environment variable is set).

[DonJayamanne]

Solution:

• Add (vscode) file monitor for local workspace
• If a file/folder is created, and check if we have an interpreter in there
  Use lookForInterpretersInDirectory
• If there are no interpreters, then get out.
• If we have an interpreter, then raise an event indicating the fact interpreters need to be refreshed
• Add a handler for the above event in the CacheableLocatorService
• In the event handler, clear the map promisesPerResource