Issue #1937600 by Berdir, rootatwc | webchick: Determine what services to register in the new Drupal class.

Issue #1950326 by swentel: Fixed Entity displays are not renamed/deleted when a bundle is renamed/deleted.

Issue #1935970 by msonnabaum, dawehner, RobLoach: Convert timer_* to a utility class and convert tests to phpunit.

Issue #1925738 by tim.plunkett: Followup: Convert language's system_config_form() to SystemConfigFormBase.

Issue #1954246 by Wim Leers: Fixed Underlying content visible in the editing area while using PropertyEditor widget that uses padding.

Issue #1898448 by julien, drupalway, podarok, jenlampton, steveoliver, joelpittet, jwilson3, chrisjlee, Cottser | c4rl: Convert search module to Twig.

Issue #1945326 by tim.plunkett: Rename \Drupal\system\Tests\System\SystemConfigFormBase to \Drupal\system\Tests\System\SystemConfigFormTestBase.

A little bit too much...

This reverts commit aab7094c.

Issue #1876964 by dawehner, tim.plunkett: Improve DX when writing style plugins by adding a renderSingle function.

Issue #1953832 by xjm, David_Rothstein: Replace 'target type' on entity reference field settings with something clearer.

Issue #1948884 by vijaycs85, YesCT, Gábor Hojtsy: Create configuration schemas for block and custom_block() modules.

Issue #1833126 by micnap, mgifford, YesCT, craychee: Add more semantic representation of original language in translations UI.

Issue #1561362 by Niklas Fiekas, chrisdolby, mtift: Change file_transfer() to use BinaryFileResponse.

Issue #1939024 by Alan Evans, mtift, Crell: Convert action_admin_manage() to a new-style Controller.

Issue #1801356 by dawehner, disasm, amateescu, effulgentsia: Entity reference autocomplete using routes.

Issue #1945418 by tim.plunkett, jaskho: Fixed New-style placeholders in menu_router() table break breadcrumbs, menu tree, etc.

Issue #1847084 by jessebeach, trawekp, LewisNyman, nod_, tarekdj: Fixed Vertical toolbar doesn't work with overlay (measure/track displacing elements better + provide change events for them).

Revert "Issue #1938980 by Crell, rootatwc, tim.plunkett: Move controller derivation to route enhancers."

Temporary rollback; this broke AJAX paths. Working on better test coverage.

This reverts commit 221099b5.