Investigate/eliminate barrel files

[swissspidy]

Task Description

Barrel files can slow down your build/tests, can cause circular dependencies, and makes tree shaking more difficult.

Admittedly, we have a lot of those in the code base.

I was wondering whether we could use something like eslint-plugin-no-barrel-files to detect barrel files in in the project to see where they currently have a negative impact.

They might not have an impact on our actual bundle size due to better tree shaking, but the difference can be more significant in places like Jest unit tests.

Right now said ESLint rule reports 1502 problems.