Bug: Altering variables with "@use with" can lead to issues when trying to configure values multiple times

[NickDJM]

Summary

If you include a file using @use ... with(); you can run into an issue if multiple files try to alter the same source file (see width utilities in the navigation shelf package).

We might be able to resolve this issue, but it will require a huge flow change.

The Sass docs literally mention this use-case with altering values after members are loaded.

https://sass-lang.com/documentation/at-rules/use/

Steps to reproduce

1. Add your own customizations to the width utilities
2. Include the navigation-shelf package
3. Break everything and be sad

Expected Behaviour

Multiple packages should be able to alter the same utility generation

[NickDJM]

This would be a good opportunity to implement private variables as well instead of calling things "base"

[NickDJM]

We're going to implement private variables, but the refactor to configure stuff would be huge. I'm not saying this will never happen, but it will be re-addressed down the road I think.