Issue #2466585 by Wim Leers, Fabianx: Decouple cache implementation from the renderer and expose as renderCache service

Issue #2468151 by lhangea, rpayanm, Palashvijay4O: Rename the CacheContexts service to CacheContextsManager

Issue #2459155 by alexpott, pfrenssen, hussainweb, neclimdul: Remove REQUEST_TIME from bootstrap.php

Issue #2453059 by Wim Leers: Set default render cache contexts: 'theme' + 'languages:' . LanguageInterface::TYPE_INTERFACE

Issue #2451679 by Wim Leers, dawehner: Validate cache contexts (+ cache contexts in some views plugins wrong)

Issue #2381217 by Wim Leers, dawehner, Fabianx: Views should set cache tags on its render arrays, and bubble the output's cache tags to the cache items written to the Views output cache

Issue #2378883 by Wim Leers, dawehner: Convert existing drupal_render() KernelTestBase tests to PHPUnit tests