Merge branch '6.4' into 7.0

* 6.4: (32 commits)
  [Validator] Fix registering "is_valid()" for `#[Expression]`
  [Scheduler] Trigger unique messages at runtime
  [Scheduler] Fix CHANGELOG
  [Clock] Add `DatePoint`: an immutable DateTime implementation with stricter error handling and return types
  [Scheduler] Allow modifying the schedule at runtime and recalculate heap
  [Cache] Fix Redis6Proxy
  [Finder] Disable failing test about open_basedir
  Fix merge
  Fix merge
  Minor CS fixes
  Deprecate `Kernel::stripComments()`
  Remove setAccessible reflection call in tests
  [Notifier] Telegram Bridge add escaping for \
  [Component][AssertMapper] add type hint of an argument in asset mapper command
  [Translation] [Phrase] Refacto ReadConfig and WriteConfig into arrays
  [Routing] Fix routing collection defaults when adding a new route to a collection
  [Messenger] Fix cloned TraceableStack not unstacking the stack independently
  [Translation] Add `--as-tree` option  to `translation:pull` command
  [Mime] Allow to add some headers as a strings
  [Translation] Give current locale to locale switcher runWithLocale callback
  ...

Author: nicolas-grekas

Tests/Extension/Validator/ViolationMapper/ViolationMapperTest.php

@@ -13,7 +13,6 @@
 
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\EventDispatcher\EventDispatcher;
-use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\Form\CallbackTransformer;
 use Symfony\Component\Form\Exception\TransformationFailedException;
 use Symfony\Component\Form\Extension\Core\DataMapper\DataMapper;

Tests/FormFactoryTest.php

@@ -16,7 +16,6 @@
 use Symfony\Component\Form\Extension\Core\Type\TextType;
 use Symfony\Component\Form\FormFactory;
 use Symfony\Component\Form\FormRegistry;
-use Symfony\Component\Form\FormRegistryInterface;
 use Symfony\Component\Form\FormTypeGuesserChain;
 use Symfony\Component\Form\FormTypeGuesserInterface;
 use Symfony\Component\Form\Guess\Guess;