Issue #2095195 by yched, fago, Berdir, amateescu, swentel, pfrenssen, Xano: Remove deprecated field_attach_form_*().
Issue #2050835 by Berdir | yched: Move Widget, Formatter, and FieldType plugin types to the Core\Field system.
Issue #2051923 by Berdir, dixon_, plach: Rename \Drupal\Core\Entity\Field\Field, related subclasses and interfaces to *FieldItemList.
Issue #2021817 by effulgentsia, yched: Make widgets / formatters work on EntityNG Field value objects.
Issue #1846648 by yched, swentel: Rename field_attach_submit(), because it is also called from within validation.
Issue #1785256 by yched, Stalski, zuuperman, sun, tstoeckler, aspilicious, EclipseGc, larowlan: Widgets as Plugins.