Issue #3262190 by daffie, longwave: Add miscellaneous return type hints for Symfony 6

core/lib/Drupal/Core/ProxyClass/Routing/MatcherDumper.php

core/lib/Drupal/Core/Render/HtmlResponse.php

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

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

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

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

core/lib/Drupal/Core/Session/SessionManager.php

...ore/TypedData/Validation/ContextualValidatorInterface.php

...ore/TypedData/Validation/RecursiveContextualValidator.php

...es/big_pipe/tests/src/Unit/Render/ManyPlaceholderTest.php

...s/help/tests/modules/help_test/src/SupernovaGenerator.php

core/modules/jsonapi/src/Serializer/Serializer.php

...rest/tests/src/Unit/Plugin/views/style/SerializerTest.php

...tests/serialization_test/src/SerializationTestEncoder.php

...tests/modules/session_test/src/Session/TestSessionBag.php

...dules/system/tests/src/Functional/Routing/MockMatcher.php

...ependencyInjection/Dumper/OptimizedPhpArrayDumperTest.php

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

core/tests/Drupal/Tests/Core/Session/SessionManagerTest.php

.../Tests/Core/StackMiddleware/NegotiationMiddlewareTest.php