Issue #2849669 by alexpott, pwolanin, Munavijayalakshmi, dawehner: Fix \Drupal\Component\Utility\Unicode() because of the Symfony mbstring polyfill

Issue #2612334 by NickWilde: Remove dead code in \Drupal\Core\Asset\[Css|Js]Collection[Grouper|Optimizer]

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

Issue #1392754 by tss, justAChris, jhodgdon: Comply with new documentation standards for @file for namespaced class files

Issue #1833356 by grendzy: CSS files encoded in UTF-8 with BOM break the design when enabling CSS aggregation

Issue #2400287 by hass, cutesquirrel, borisson_, rteijeiro, pfrenssen, cilefen: Remove all occurences of sourceMappingURL and sourceURL when JS files are aggregated

Issue #352951 by Wim Leers, mfer, mcjim, larowlan, RobLoach, sdboyer, Owen Barton, JohnAlbin: Make JS & CSS Preprocessing Pluggable.