Issue #2083947 followup by echoz: System.module: Update use of icons to new standards.
Issue #2126973 by damiankloip: FATAL error in Drupal\field\Plugin\views\field\Field::groupByForm.
Issue #2127487 by chx: GetStringTranslationStub() ignores variables.
Issue #2019055 by plach, fago, kfritsche: Switch from field-level language fallback to entity-level language fallback.
Revert "Issue #2019055 by plach, fago, kfritsche: Switch from field-level language fallback to entity-level language fallback."

This reverts commit 46942cd373e815d2bb994c5b0615352abbdf4c90.
Issue #2019055 by plach, fago, berdir, yched, Gábor Hojtsy, kfritsche, jibran: Switch from field-level language fallback to entity-level language fallback.
Issue #2125043 by Sutharsan: Remove  '#type' => 'markup'.
Issue #2084463 by dawehner, pwolanin, David_Rothstein, tim.plunkett, Xano: Convert contextual links to a plugin system similar to local tasks/actions.
Issue #1859684 by dawehner, effulgentsia: Expand routeBuilder unit test.
Issue #2105939 by Wim Leers, vijaycs85: Make sure all YML files in Editor module has no type-casting to string + config system changes broke image uploading in editors.
Issue #1443606 by claudiu.cristea: Alt, title, width and height for default images.
Issue #700696 by claudiu.cristea, willvincent, swentel, pyrollo, StepanKuzmin: Add 'flush' back into image module.
Issue #2125407 by moshe weitzman: Don't redirect CLI requests to install.php.
Issue #2100073 by dawehner: Convert local_actions() to the new local action plugins.
Issue #2090541 by plopesc, yched: Avoid storing numeric target_id()'s for default values in field instance CMI files.
Issue #1810350 by plach, kfritsche, boran, YesCT: Remove menu_* entity keys and replace them with entity links.
Issue #2100571 by tim.plunkett: Do not add normalize.css to stark.
Issue #2120851 by swentel: UI glitch in Add Content.
Issue #2124177 by juampy: Typo in docblock.
Issue #2129197 by dawehner: Testbot (run-tests.sh with --file) attempts to run non-test classes, fails.