Issue #2570285 by mr.baileys, cpj, stefan.r, alexpott, nlisgo, joelpittet, Aki Tendo, borisson_, chx, dawehner, s_leu, Berdir: Make sure TranslatableMarkup accepts string values only

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

Issue #2571695 by dawehner, plach, stefan.r, jaredsmith, lauriii, YesCT, xjm, catch, alexpott, joelpittet, Ryan Weal, Sutharsan, subhojit777, justAChris, nlisgo, effulgentsia, rpayanm, larowlan, chx, geertvd: Remove !placeholder and unsafe string return from SafeMarkup::format()

Issue #2570107 by alexpott: Make format_plural() return a PluralTranslatableString object to remove reliance on a static, unpredictable safe list

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

Issue #2557113 by stefan.r, alexpott, dawehner, joelpittet, cilefen, lauriii, plach, catch, chx, xjm: Make t() return a TranslationWrapper object to remove reliance on a static, unpredictable safe list

Issue #2562487 by stefan.r, chx, tim.plunkett, dawehner, alexpott: Get better error reporting from __toString

Issue #697760 by sun: Replace getInfo() in tests with native phpDoc + annotations (following PHPUnit).

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

Issue #2111349 by dawehner, tim.plunkett: Move format_plural to the string translation service and format_interval to the date service.