Issue #2853503 by Aki Tendo, alexpott, larowlan, Wim Leers, klausi, fgm, dawehner, mondrake, catch, Berdir, neclimdul, borisson_: Remove all assert('string') calls from Drupal core because deprecated in PHP 7.2

Issue #2879512 by bkosborne: Path aliases can be forgotten after a cache rebuild due to race condition in CacheCollector

Issue #2776975 by joelpittet, dawehner, tim.plunkett, xjm, pfrenssen: March 3, 2017: Convert core to array syntax coding standards for Drupal 8.3.x RC phase

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2501191 by jhedstrom: CacheCollector can result in an exception is cid + classname is too long to be used as a lock name

Issue #2454649 by Aki Tendo, dawehner: Cache Optimization and hardening -- [PP-1] Use assert() instead of exceptions in Cache::merge(Tags|Contexts)

Issue #2340123 by Wim Leers: Setting cache tags can be tricky: use strings instead of nested arrays to improve DX.

Issue #2169447 by damiankloip, sun, longwave: DX: Supply CacheBackendInterface::CACHE_PERMANENT as Cache::PERMANENT.

Issue #1858616 by Berdir: Extract generic CacheCollector implementation and interface from CacheArray.