Allow port settings to take a range of ports

[gadenbuie]

If port access is controlled in the environment running VS Code, users can set the port-related options to a fixed port to an allowed, open port. However, if the user has multiple VS Code instances open, they are limited to running one Shiny application at a time at the fixed port address.

We could update shiny.python.port, shiny.r.port and shiny.python.autoreloadPort to accept a range or array of ports:

"shiny.python.port": "8010-8020,8123",

The syntax could be {start}-{end} for start through end (inclusive) or comma separated values. The above would include ports 8010, 8011, ..., 8020, and 8123.

This would give system administrators the ability to open a limited range of ports, while allowing multiple apps to be run simultaneously.