Issue #2166915 by ianthomas_uk, sun | plach: Remove uses of deprecated language functions in tests and procedural code.

Issue #1862202 by plach, Berdir, katbailey, ParisLiakos, alexpott, chx, sun, larowlan, Gábor Hojtsy, cosmicdreams, vijaycs85, YesCT, penyaskito, andypost, Albert Volkman, joelpitett: Objectify the language system.

This caused a conflict in the language objectification patch. Postponing.

This reverts commit 9e017ada.

Issue #2074037 by Wim Leers, effulgentsia: Add drupalPostUrl() — drupalPost()/drupalPostAjax() are for forms only, D8 JS performs non-form HTTP requests.

Issue #1754246 by webflo, swentel, penyaskito, andypost, alexpott, YesCT, dagmar: Languages should be configuration entities.

Issue #1826252 by Jeroen, benjf, wilco: Domain language negotiation broken when a base url is configured.

Issue #1888424 by katbailey, steveoliver, twistor, beejeebus, effulgentsia: Change notice: Make Drupal's URL generation logic available to HttpKernel, and minimize code repetition/divergence.

Issue #1899994 by katbailey, plach, YesCT: Fixed Disentangle language initialization from path resolution.

Issue #1714462 by n3or, sun, Gábor Hojtsy: Convert language negotiation settings to configuration system.

Issue #1645156 by attiks, tstoeckler, Albert Volkman, Carsten Müller, Sweetchuck: Fixed URL generation only works on port 80.

Issue #1711070 by kid_icarus, tim.plunkett, xjm, droplet, zendoodles and cam8001: Convert tests to use ::$modules property instead of parent::setUp($modules).