(cherry picked from commit ed8ceb79)
(cherry picked from commit 5fd082b6)

Issue #2466197 by alexpott, heddn, Crell, dawehner, pjcdawkins, catch: Staging directory should not have to be writeable

Issue #1377740 by jbrown, bvanmeurs, catch, anrikun, Jorrit, rpayanm, mvc, mikeytown2, chx: file_unmanaged_move() should issue rename() where possible instead of copy() & unlink()

(cherry picked from commit 26cf55bb)

Issue #2721887 by snehi, Sonal.Sangale, gaurav.pahuja, Ashish.Dalvi, jhodgdon, joachim, Mile23: Docs topic 'File interface' contains obsolete data

(cherry picked from commit 86927782)

Issue #2571845 by drupal.ninja03, hussainweb, anil280988, snehi, jhodgdon, GoZ, stefan.r: Links to wikipedia/php.net should be part of the actual t() string so they can be localized

Issue #1443342 by joseph.olstad, mikeytown2, xjm, joelpittet, brianV, effulgentsia: Inline file_uri_scheme() in file_stream_wrapper_uri_normalize() and other file.inc functions

Issue #2487588 by YesCT, Leksat, Schnitzel, alexpott, anavarre, xjm: Move CMI import/export directory "staging" to "sync", as it is confused with staging environments

Issue #2487592 by alexpott, JeroenT, Schnitzel, cilefen: CMI: don't ship with a default "active" directory that is empty in most Drupal installations

Issue #2557519 by alexpott, joelpittet: Remove many usages SafeMarkup::checkPlain() and replace with Html::escape()

Issue #2382859 by rpayanm, mondrake, ianthomas_uk: Remove file_stream_wrapper_get_*() and file_get_stream_wrappers()

Issue #2392559 by mondrake, mitrpaka, JeroenT, rpayanm, adci_contributor, ianthomas_uk: Remove all uses of file_stream_wrapper_get_* and file_get_stream_wrappers

Issue #2491155 by mikeburrelljr, Mac_Weber, opdavies: Update drupal.org and kernel.org URLs in core modules (Follow-up to 2489912)

Issue #2432791 by alexpott, vijaycs85, tim.plunkett, joshtaylor, Fabianx, Berdir, yched, bojanz: Skip Config::save schema validation of config data for trusted data.

Issue #2457887 by prateekMehta, stefan.r, rpayanm, alexpott: Use Utility\SafeMarkup class instead of Utility\String for placeholder(), checkPlain(),format() functions

Issue #2050759 by tim.plunkett, fietserwin: Move drupal_chmod and other code in file.inc to a Drupal\Core\File\FileSystem class

Revert "Issue #2388749 by alexpott, adci_contributor, ParisLiakos: Register symfony's mime guessers if they are supported"

This reverts commit 4dae1d99.

Issue #2388749 by alexpott, adci_contributor, ParisLiakos: Register symfony's mime guessers if they are supported

Issue #2392319 by alexpott, effulgentsia: Config objects (but not config entities) should by default be immutable

Issue #2393455 by slashrsm, RavindraSingh: Wrong arguments sent to LoggerInterface::error() from file_unmanaged_move()

Issue #2353357 by Berdir: hook_stream_wrappers_alter() is broken since modules are not loaded on demand, also change to an event since it's the last hook that forces this during bootstrap

Issue #2170235 by Berdir, penyaskito, larowlan, alexpott, sushyl: file_private_path should be in $settings, like file_public_path

Issue #2276203 by webflo, lauriii, nlisgo, kallehauge, Snipon: Fixed CSS Aggregation breaks URLs with Query String.

Issue #2028109 by tim.plunkett, almaudoh, twistor, larowlan, slashrsm, Berdir, Arla, neclimdul, Cottser: Convert hook_stream_wrappers() to tagged services.

Issue #2112247 by sihv, dgroene, aalamaki, Dennis Walgaard, mErilainen: Fixed Valid file extensions in file names are not properly enforced when uploading files.

Issue #2297947 by amitgoyal, andrewmacpherson: Clean up API docs for hook_file_mimetype_mapping_alter().

Issue #1914914 by purdy_nc, meba, chx, heyrocker: Add to docs of file_scan_directory to discuss excluding config

Issue #1921558 by ParisLiakos, xjm, Dave Reid: Convert file_get_mimetype() to use Symfony MimeTypeGuessers.

Issue #2003800 by jhedstrom, filijonka, YesCT, ParisLiakos, steeloctopus, damiankloip, sun, LinL, amateescu: Move drupal_check_memory_limit() and parse_size() functionality to components.

Issue #2221695 by brantwynn, ianthomas_uk, grom358, ParisLiakos, Jalandhar: Remove uses of deprecated URL functions.