Refactor interpreter discovery

[kimadeline]

Make it harder, better, faster, stronger in its own module.

[karthiknadig]

Handle this case when refactoring: #8509

[raratiru]

I landed here because in my setup, python and pipenv executables are correctly recognized according to my settings.json:

{
   ...
    "python.pipenvPath": "/home/user/.local/bin/pipenv",
    "python.pythonPath": "${workspaceFolder}/.venv/bin/python"
}

However, I have to manually re-select the same (already recognized) interpreter Python 3.8.6 64-bit ("myenv": pipenv).

Otherwise, when vscode automatically asks to install pylint for example, the command issued will not be the expected:

pipenv install pylint --dev.

It will be:

/home/user/project/.venv/bin/python /home/user/.vscode/extensions/ms-python.python-2020.12.424452561/pythonFiles/pyvsc-run-isolated.py pip install -U pylint

$ uname -a
Linux House 5.4.0-0.bpo.4-amd64 #1 SMP Debian 5.4.19-1~bpo10+1 (2020-03-09) x86_64 GNU/Linux

$ code --version
1.52.1