Set PYTHONPATH in VS Code Settings

If project uses VS Code integration, render `terminal.integrated.env.{PLATFORM}` setting in `.vscode/settings.json` with `PYTHONPATH`containing paths to dependencies.

This will allow users to import these dependencies from the VS Code integrated terminal just like in their code.

See [Use of the PYTHONPATH variable](https://code.visualstudio.com/docs/python/environments#_use-of-the-pythonpath-variable) for more details.

Start with the VS Code integration that renders `.vscode/settings.json` and review the linked VS Code documentation on `PYTHONPATH`. Determine how dependency paths are gathered and how platform-specific `terminal.integrated.env.{PLATFORM}` settings are emitted. Done means the generated settings expose those dependencies through `PYTHONPATH` in the integrated terminal.

Written by the indexing model from the issue text.