Issue #2576533 by alexpott, stefan.r, Wim Leers, dawehner, xjm, effulgentsia, catch: Rename SafeStringInterface to MarkupInterface and move related classes

Issue #2569069 by stefan.r, mr.baileys, alexpott, lauriii: Replace TranslationWrapper with TranslatableString and deprecate TranslationWrapper

Issue #1392754 by tss, justAChris, jhodgdon: Comply with new documentation standards for @file for namespaced class files

Issue #2299677 by er.pushpinderrana, gauravkhambhala | jhodgdon: Fix up annotation-related topics a bit.

Issue #2216541 by jhodgdon, Gábor Hojtsy: Fill in topic/@defgroup docs for Internationalization overview.

Issue #2244447 by alexpott, sun, Berdir: Translation of low-level info/annotations leads to circular dependencies.

Issue #2079797 by ParisLiakos, Xano, amateescu, tim.plunkett: Provide a trait for $this->t() and $this->formatPlural().

Issue #2005716 by tim.plunkett, msonnabaum, dawehner, alexpott, effulgentsia: Promote EntityType to a domain object.

Issue #1969970 by dawehner, jhodgdon, webchick, EclipseGc, tim.plunkett: Documentation for translatable plugin properties on annotations

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

- Patch #1683644 by chx, EclipseGc, tim.plunkett, aspilicious, xjm, dawehner, effulgentsia: use Annotations for plugin discovery.