Prefer using `conda list -n/-p --json` over string and parsing

[DonJayamanne]

Conda list supports the json format, since 2015-16 (tests were added in 2017 for this arg).
https://docs.conda.io/projects/conda/en/stable/release-notes.html#id531
I think we should use that over parsing the string based on spaces and looking for package name and version.

Would have also prevented #416 (comment)

[eleanorjboyd]

Hello! This fix is now out on python-environment-extension version 1.17.10341640 (the newest pre-release). To switch, go to the marketplace for this extension and either select to install the latest pre-release or click the button that says "switch to pre-release" for the extension version. We would appreciate greatly if you are able to give this a try on the pre-release version and let us know if your bug is fixed!