Revert "Issue #2683435 by hussainweb, mikeryan, quietone, alexpott, michael_wojcik, phenaproxima, benjy: Consider renaming Migrate's cckfield plugins"

This reverts commit 24f816a1.

Issue #2683435 by hussainweb, mikeryan, quietone, alexpott, michael_wojcik, phenaproxima, benjy: Consider renaming Migrate's cckfield plugins

Issue #2787619 by hussainweb, phenaproxima, alexpott: CckMigration does not type hint CckPluginManager correctly

Issue #2787639 by hussainweb: MigrateCckFieldPluginManager mixes up its behaviour for creating and loading definitions

Issue #2225775 by vasi, quietone, phenaproxima, chx, penyaskito, mikeryan, esclapes, vprocessor, steinmb, Gábor Hojtsy, Marc Angles, bwinett: Migrate Drupal 6 core node translation to Drupal 8

Issue #2700581 by mikeryan, benjy, heddn, vasi: Destination bundle set in destination plugin, not in process

Issue #2631736 by quietone, jmuzz, Sam152, svendecabooter, benjy: Cckfield Plugins must distinguish core versions

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2666650 by alexpott, benjy: Inject migration and source plugin managers into the migration plugins

Issue #2625696 by chx, benjy, alexpott, catch, mikeryan, andypost, phenaproxima: Make migrations themselves plugins instead of config entities

Revert "Issue #2625696 by chx, alexpott, benjy, mikeryan, andypost, phenaproxima: Make migrations themselves plugins instead of config entities"

This reverts commit 694994fe.

Issue #2625696 by chx, alexpott, benjy, mikeryan, andypost, phenaproxima: Make migrations themselves plugins instead of config entities