Remove synchronous process launches

[DonJayamanne]

In configSettings.ts we have some code that launches python processes synchronously.
// const output = child_process.execFileSync(pythonPath, args, { encoding: 'utf8' });
This slows down other extensions when loading Python extension.

If user is working purely on python extension, then I guess this is ok to have.
However consider the following scenario:

• User loads a Jupyter Notebook
• Jupyter notebook activates python extension
• Now Python extension runs some code synchronously, thereby blocking other extensions such as Jupyter from running - i.e. Jupyter looks slow in opening Jupyter Notebooks.

Removing this code improves the load times of Jupyter notebooks significantly.

Related upstream issue causing serious perf issues in Jupyter Notebooks microsoft/vscode-jupyter#5211
Basically Jupyter Notebooks takes 20-30 seconds to load and we're trying to address that.

[karthiknadig]

@DonJayamanne Do we need to run python there to check if it is valid? I feel like an file exists check should be enough for the variety of cases it handles there.

[brettcannon]

A file check should be fairly cheap compared to executing Python itself.

[DonJayamanne]

I feel like an file exists check should be enough for the variety of cases it handles there.

Sure thats much better, is there a way we can do this even without a synchronous file check (sync = still blocking node process, though its a significant improvement)

[karthiknadig]

I have looked into that class before. Turning functions in the class to async is something we need to do in the long term. Since most of the APIs in that class are all sync, changing any one of them to async especially something so fundamental like pythonPath cause significant async creep across the extension.

I would say, give it a try to make that async, but if you see that it is creeping into too many places, then we can just do the sync version.