* [ refactor ] moving Data.OpenUnion to base
* [ new ] System.Concurrency.(Linear/Session)
* [ test ] for the new feature
Fixing other tests impacted by the refactoring
* [ cleanup ] move definitions around, touch up docs
* [ fix ] re-export linear notations for Control.Linear.LIO
* Emit warning for fixities with no export modifiers
This is to help update all the existing code to program with explicit
fixity export directives in preparation for the behavioral change where
they will become private by default.