Stubs flag package name mapping

I'm setting up a devcontainer with vscode and using circup to allow some local dev and noticed the stubs flag but it fails on a couple packages.

If your project uses `adafruit_button` or `adafruit_bus_device` they won't remap to the package in PyPi.

Could a reverse of https://github.com/adafruit/circup/blob/53ac85b2c3e1271d0ff50bdbd317ead14afe5432/circup/command_utils.py#L64 be added?

I'm happy to do a PR, still pretty new to Python so not sure on preferred way but had a couple ideas.

1. Add flag to existing function to do inverse map.
2. Add new function that does inverse mapping.
3. Move the package map dict to a const which can be used by two functions.

Start by reading `circup/command_utils.py`, especially the package mapping linked in the issue, and trace how the stubs flag uses it. Done means the stubs flag maps `adafruit_button` and `adafruit_bus_device` to their PyPI package names.

Written by the indexing model from the issue text.