Issue #2294439 by dawehner, sun | neclimdul: Add vfsStream library for filesystem mocking in unit tests.
Issue #2306165 by a_thakur: Remove user_authenticate().
Issue #2306545 by a_thakur: Remove views_plugin_list().
Issue #2306469 by a_thakur: Remove views_fetch_plugin_names().
Issue #2306611 by rbayliss: Fixed Field weights are not respected on render.
Issue #1533250 by YesCT, fran seva, TravisCarden, xjm, sriharsha.uppuluri | NROTC_Webmaster: Many coding standards clean-ups in locale module.
Issue #2299427 by tim.plunkett, amitgoyal, joshi.rohit100: Remove drupal_build_form() once all its usage is removed as it is deprecated.
Issue #2306429 by KarlKedrovsky, a_thakur: Remove user_access().
Issue #2146035 by olli, mondrake: Fixed drupalSettings.path.pathPrefix does not contain the language identifier.
Issue #2306703 by realityloop | YesCT: Docs update from Clean up LocaleConfigManager / TypedConfigManager features and cache duplications.
Issue #2304461 by sun: KernelTestBaseNG™.
Performance: Use shared fixtures for all tests in a class.
Fixed $this->container is not synced across kernel rebuilds.
Fixed container rebuild does not persist request stack.
Added tearDownAfterClass() + assert enableModules() post-conditions.
Reverted shared fixtures approach; leverage compiled container instead.
Relocated KernelTestBase methods.
Replaced cloned ContainerBuilder copy with actually compiled Container.

Also register test class as a logger.
Added alternative setUp() variant of cloned, empty ContainerBuilder.

DrupalKernel::setContainer() before boot() turned out to be key solution
for rebooting a kernel with an already prepared service container.
Enable drupal_render() + _theme().