Forbid wildcard exports

[mcmire]

When developing and maintaining a package, it is critical to understand what modules are being exported. There are a couple ways to do this. One way is to add a test for the entry point, like for utils. Another, more obvious way is to be explicit about which modules are being exported in the entrypoint. Currently we allow wildcard exports. I am proposing we stop doing this and instead prefer named exports.

No ESLint rule exists per se to forbid wildcard exports, but evidently you can use no-restricted-syntax as a workaround as described here: import-js/eslint-plugin-import#2493 (comment)

[mcmire]

We should implement this in core first before adding it to this repo.