* Added`ControllerTrait::isFormValid()`

* Added an`help_html` form option to display the`help` text as HTML

* Deprecated the "Psr\SimpleCache\CacheInterface" / "cache.app.simple" service, use "Symfony\Contracts\Cache\CacheInterface" / "cache.app" instead

*[BC Break] When using Messenger, the default transport changed from

using Symfony's serializer service to use`PhpSerializer`, which uses

PHP's native`serialize()` and`unserialize()` functions. To use the

original serialization method, set the`framework.messenger.serializer.id`

config option to`messenger.transport.symfony_serializer`.

* Added`SuggestMissingPackageSubscriber` for suggesting missing packages when using console commands

4.2.0