As a Tuleap Developper, I want to split the big "validate-service.js" file into multiple smaller files. Ideally, each tracker "field" would have its own "value-formatter" responsible for correctly formatting the field value into an object that the REST API can handle.

Usually, that means returing only "field_id" and "value".

Doing this will help us advance request #13057 as each "split" file will be an ES module.