Introduce composer.json files for Drupal\Component\*

During the Drupal 8 development cycle a number of stand alone components have been successfully created. Part of the discussion around the creation of these components was that we could ultimately begin sharing these components with the php community at large. PHP has largely embraced the composer based approach which requires a composer.json file to reside at the base of the component code's directory structure. There is no impact for anyone except core developers writing new components. The ongoing requirement should be to legitimately make any code in Drupal/Component always stand-alone or at worst dependent upon other code within Drupal/Component and all Components should provide a composer.json file.