Issue #3233047 by daffie, longwave, dww, larowlan, Kristen Pol: Drupal\Core\Routing\RequestContext::fromRequest() should be returning $this

Issue #2917331 by catch, martin107, Deepak Goyal, longwave, andypost, ravi.shankar, alexpott, daffie, larowlan: Decouple from Symfony CMF

Revert "Issue #2917331 by catch, martin107, Deepak Goyal, longwave, andypost, ravi.shankar, daffie, larowlan: Decouple from Symfony CMF"

This reverts commit 98eed2b1.

Issue #2917331 by catch, martin107, Deepak Goyal, longwave, andypost, ravi.shankar, daffie, larowlan: Decouple from Symfony CMF

Issue #2822190 by webflo, Wim Leers, dawehner, alexpott, effulgentsia, SchnWalter: PathValidator validates based on a RequestContext leaked from the current request, resulting in false negatives during CLI requests and POST submissions

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

Issue #2619700 by tim.plunkett: \Drupal\Core\Path\PathValidator::getPathAttributes() does not catch MethodNotAllowedException

(cherry picked from commit 438713de)

Issue #2509300 by dawehner, catch, larowlan: Path alias UI allows node/1 and /node/1 as system path then fatals

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

Issue #2417647 by Wim Leers, effulgentsia: Add leading slash to paths within 'user-path:' URIs, to allow 'user-path:' URIs to point to the <none> route

Issue #2343759 by pwolanin, larowlan, dawehner, tim.plunkett, effulgentsia, xjm, Wim Leers: Provide an API function to replace url()/l() for external urls.

Issue #2322809 by chx, dawehner, tim.plunkett: Tighten routing security by access checking in matchRequest.

Issue #2310705 by lokeoke, tim.plunkett, dawehner: AccessManager should introduce constants for 'ANY' / 'ALL'.