Issue #2457887 by prateekMehta, stefan.r, rpayanm, alexpott: Use Utility\SafeMarkup class instead of Utility\String for placeholder(), checkPlain(),format() functions

Revert "Revert "Issue #2457653 by Gábor Hojtsy: System.site langcode is both used as a file language code and a site language code""

This reverts commit 079a52b4.

Revert "Issue #2457653 by Gábor Hojtsy: System.site langcode is both used as a file language code and a site language code"

This reverts commit 364a6e9c.

Issue #2457653 by Gábor Hojtsy: System.site langcode is both used as a file language code and a site language code

Issue #2286971 by znerol, Berdir, almaudoh, cilefen: Remove dependency of current_user on request and authentication manager

Issue #2364157 by mpdonadio, dawehner, martin107, Berdir, pcambra, naveenvalecha, tim.plunkett: Replace most existing _url calls with Url objects

Issue #2395395 by alexpott, effulgentsia, Gábor Hojtsy: TestBase lacks a config method to be used consistently in tests

Issue #2318787 by jarsenx | melbs: Basic_auth Module:  Fix documentation that refers to enabling/disabling of modules.

Issue #2343661 by larowlan, tim.plunkett | xjm: Rename l() to _l() and url() to _url(), and document replacements.

Issue #2339435 by YesCT, alexpott: Default no longer needs to be a property on Language or ConfigurableLanguage.

Issue #2336177 by alexpott, YesCT: Fixed ConfigurableLanguage cannot be created/removed directly, integrate language_save() and language_delete().

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

Issue #2183113 by jhodgdon, effulgentsia, tim.plunkett, herom, larowlan: Update hook_help signature to use route_name instead of path.

Issue #2103035 by batigolix, jhodgdon, clemens.tolboom: Review/update hook_help() for the basic_auth module.

Issue #2041885 by BTMash, cweagans, klausi: Move HTTP basic authentication provider to a separate module.