Package Files Bundled Outside Package Folder

Discovered in [#1234](https://github.com/adafruit/circuitpython/issues/1234).

When files are in a package folder, but the `package_folder_prefix` doesn't match the package foldername, the files are bundled outside of the package folder.

Start by locating the bundling logic that handles package_folder_prefix and reproduce the case where it differs from the package folder name. Trace which files are placed outside the package folder, then verify that the same files remain inside it when the prefix does not match.

Written by the indexing model from the issue text.