#4247512 Split `lib/products-values`

lib/products-values is currently a large monolith, consisting of many different imports and exports. This makes it hard for the bundler to tree-shake effectively, and introduces potential problems because of circular dependencies between lib/products-values and lib/plans, for example.

This PR splits the library into many small modules, while re-exporting everything from the index file. This should result in minimal changes in consumers of this library, while enabling better tree-shaking.

I don’t expect immediate performance benefits from this PR, as there are likely other large libraries to untangle first. I was wrong; see the comments below.

This PR is working towards the end goal of removing the dependency on lib/plans from the critical path, which may yet turn out to be impossible.

Changes proposed in this Pull Request

• Split the various exports in index.js into individual modules
• Split assertValidProduct into a new utils/ folder
• Move all of the translated constants from constants.js to a new translations.js
• Add package.json with sideEffects config, to enable the bundler to take advantage of the modularisation of the library
• Ensure lib/plans and lib/domains refer to the new individual modules instead of the index file, to avoid circular dependencies

Testing instructions

This PR doesn’t change any functional code, it only moves some code around. As such, a correct build and passing automated tests should be enough to ensure that nothing got broken.