Issue #1903346 by Berdir, tim.plunkett, EclipseGc: Establish a new DefaultPluginManager to encapsulate best practices.

Issue #1818570 by Berdir, effulgentsia, das-peter, andypost: Convert users to the new Entity Field API.

Issue #1620010 by dawehner, ParisLiakos, plach, jibran: Move LANGUAGE constants to the Language class.

Issue #1967420 by tim.plunkett, dawehner: Allow Core\AnnotatedClassDiscovery to pass all parameters to the constructor of Component\AnnotatedClassDiscovery.

Issue #1818556 by das-peter, plach, fago, Berdir, vijaycs85: Change notice: Convert nodes to the new Entity Field API.

Issue #1849752 by effulgentsia, Berdir, jibran, neclimdul: Abstract non-Drupal-specific parts of AnnotatedClassDiscovery into a Drupal\Component base class.

Issue #1851706 by yched, effulgentsia, tim.plunkett: Fixed Make all core plugin managers be consistent as to whether  or ->discovery is passed to the factory.

Issue #1722882 by EclipseGc, aspilicious, tim.plunkett, fubhy, Berdir: Fixed Plugin CacheDecorator caches globally, ignores request context, and does not specify tags for cache items.

Issue #1869566 by tim.plunkett, dawehner: Allow any collection of plugins to be lazily instantiated.

Issue #1764278 by tstoeckler, tim.plunkett, yched: Fixed Run PluginManagerBase::processDefinition() in a ProcessDecorator.

Issue #1778942 by yched, tstoeckler, andypost: Fixed Discovery::getDefinition() / getDefinitions() : inconsistent return values for 'no result.
git commit -am Issue

Issue #1705702 by dawehner, damiankloip: Added Provide a way to allow modules alter plugin definitions.

- Patch #1497366 by neclimdul, effulgentsia, EclipseGc, merlinofchaos: introduce Plugin System to core.