Issue #2153891 by tim.plunkett, amateescu: Add a Url value object.

core/lib/Drupal/Component/Utility/Url.php

core/lib/Drupal/Core/Form/ConfirmFormHelper.php

core/lib/Drupal/Core/Form/FormBuilder.php

...ib/Drupal/Core/Routing/MatchingRouteNotFoundException.php

core/lib/Drupal/Core/Routing/UrlMatcher.php

core/lib/Drupal/Core/Url.php

core/lib/Drupal/Core/Utility/LinkGenerator.php

core/lib/Drupal/Core/Utility/LinkGeneratorInterface.php

...odules/menu_link/lib/Drupal/menu_link/Entity/MenuLink.php

.../modules/shortcut/lib/Drupal/shortcut/Entity/Shortcut.php

core/modules/shortcut/shortcut.module

...es/system/lib/Drupal/system/Tests/Menu/BreadcrumbTest.php

core/modules/system/system.api.php

...sts/modules/router_test_directory/router_test.routing.yml

core/tests/Drupal/Tests/Core/ExternalUrlTest.php

core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php

core/tests/Drupal/Tests/Core/Routing/TestRouterInterface.php

core/tests/Drupal/Tests/Core/Routing/UrlMatcherTest.php

core/tests/Drupal/Tests/Core/UrlTest.php

core/tests/Drupal/Tests/Core/Utility/LinkGeneratorTest.php