Issue #1897058 by disasm, rteijeiro: Replace "boolean" with "bool" when used as param/return/var type

Issue #2289917 by Wim Leers, mdrummond, lauriii, Manuel Garcia, emma.maria, Scionar, davidhernandez: Convert "messages" page element into blocks

Issue #2339491 by corbacho, dawehner, larowlan, effulgentsia, webflo: Ajax requests on forms with files fail on IE 9

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

Issue #2347469 by mondrake, Wim Leers, larowlan, kattekrab, mnico, tadityar: Rendering forms in AjaxResponses does not attach assets automatically

Issue #784626 by Wim Leers, Manuel Garcia, jcisio, joelpittet, Bevan, fcaspani, dcmouyard: Default all JS to the footer, allow asset libraries to force their JS to the header

Issue #2368797 by Wim Leers, dawehner, rteijeiro: Optimize ajaxPageState to keep Drupal 8 sites fast on high-latency networks, prevent CSS/JS aggregation from taking down sites and use HTTP GET for AJAX requests

Issue #2361681 by Wim Leers: drupal_render(): invert second argument ($is_recursive_call -> $is_root_call) => more strict, better DX/TX.

Issue #2242749 by znerol, torotil, rszrama, larowlan, dawehner, penyaskito, tim.plunkett, sun, Damien Tournoud, David_Rothstein,  effulgentsia: Fixed Port Form API security fix SA-CORE-2014-002 to Drupal 8.

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

Issue #2273277 by Wim Leers, effulgentsia, Fabianx: Fixed Figure out a solution for the problematic interaction between the render system and the theme system when using #pre_render.

Issue #2171071 by jessebeach, dawehner, chakrapani, longwave, Gábor Hojtsy, xjm, Wim Leers: Rename drupal_add_library() to _drupal_add_library() and remove its uses.

Issue #2203407 by nod_, sun: Replace #attached library array values with provider-namespaced strings.

Issue #2045927 by herom, martin107, ianthomas_uk, Xano, michaellander, Sutharsan: Replace all drupal_alter() deprecated function calls.

Issue #1996238 by sun, nod_, damiankloip, Wim Leers, longwave, alexpott, Xano, mdrummond, Mark Carver, Jeff Burnz, highrockmedia, joelpittet, et al: Replace hook_library_info() by *.libraries.yml file.

Issue #2187483 by Cottser, agentrickard, dawehner, jessebeach: Toolbar subtree is broken | JsonResponse->callback now returns data in an Insert Command without any support in ajax.js to eval the callback in the client.

Somehow this broke PHPUnit, so rolling back for now.

This reverts commit 91b465bd.

Issue #2168113 by penyaskito, jessebeach, catch: Add leading underscore and other discouragement to drupal_add_css() and drupal_add_js().

Issue #1998638 by damiankloip, dawehner, kim.pepper, cosmicdreams, alexpott, larowlan, Damien Tournoud: Replace almost all remaining superglobals (, , etc.) with Symfony Request object.

Issue #1998638 by damiankloip, dawehner, kim.pepper, cosmicdreams, larowlan, Damien Tournoud: Replace all remaining superglobals (, , etc.) with Symfony Request object.

Issue #2004086 by dawehner, pwolanin, katbailey, tim.plunkett, vijaycs85, fabpot: The Request service must be synthetic.

Issue #2107199 by Wim Leers: Allow Close(Modal)DialogCommand to remove the dialog from the DOM, document how client-side dialogs can do that too.

Issue #2049207 by dlu, blakehall, janstoeckler, ramlev, Moderate | Cottser: Replace .tpl.php with .html.twig in documentation.

Issue #1793648 by nod_, kmox83, droplet, rteijeiro: Follow-up: replace all occurence of Drupal.settings with drupalSettings.

Issue #1941288 by larowlan, effulgentsia, dawehner, nod_: Fixed Regression: ajaxPageState not being updated with AjaxResponse, assets (js/css) being added twice.

Issue #2019481 by nod_: JavaScript AJAX commands object is borked: it is shared among all Drupal.ajax instances, preventing scoped overrides.