minor #51286 Improve 6.4 UPGRADE guide (wouterj)

This PR was merged into the 6.4 branch.

Discussion
----------

Improve 6.4 UPGRADE guide

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        |

Commits
-------

ae63c18 Improve 6.4 UPGRADE guide

UPGRADE-6.4.md

@@ -9,13 +9,50 @@ BrowserKit
 Cache
 -----
 
- * `EarlyExpirationHandler` no longer implements `MessageHandlerInterface`, rely on `AsMessageHandler` instead
+ * [BC break] `EarlyExpirationHandler` no longer implements `MessageHandlerInterface`, rely on `AsMessageHandler` instead
 
 DependencyInjection
 -------------------
 
  * Deprecate `ContainerAwareInterface` and `ContainerAwareTrait`, use dependency injection instead
 
+   *Before*
+   ```php
+   class MailingListService implements ContainerAwareInterface
+   {
+       use ContainerAwareTrait;
+
+       public function sendMails()
+       {
+           $mailer = $this->container->get('mailer');
+
+           // ...
+       }
+   }
+   ```
+
+   *After*
+   ```php
+   use Symfony\Component\Mailer\MailerInterface;
+
+   class MailingListService
+   {
+       public function __construct(
+           private MailerInterface $mailer,
+       ) {
+       }
+
+       public function sendMails()
+       {
+           $mailer = $this->mailer;
+
+           // ...
+       }
+   }
+   ```
+
+   To fetch services lazily, you can use a [service subscriber](https://symfony.com/doc/6.4/service_container/service_subscribers_locators.html#defining-a-service-subscriber).
+
 DoctrineBridge
 --------------
 
@@ -27,7 +64,7 @@ DoctrineBridge
 ErrorHandler
 ------------
 
- * `FlattenExceptionNormalizer` no longer implements `ContextAwareNormalizerInterface`
+ * [BC break] `FlattenExceptionNormalizer` no longer implements `ContextAwareNormalizerInterface`
 
 Form
 ----
@@ -40,20 +77,20 @@ Form
 FrameworkBundle
 ---------------
 
- * Add native return type to `Translator` and to `Application::reset()`
+ * [BC break] Add native return type to `Translator` and to `Application::reset()`
  * Deprecate the integration of Doctrine annotations, either uninstall the `doctrine/annotations` package or disable
    the integration by setting `framework.annotations` to `false`
 
 HttpFoundation
 --------------
 
- * Make `HeaderBag::getDate()`, `Response::getDate()`, `getExpires()` and `getLastModified()` return a `DateTimeImmutable`
+ * [BC break] Make `HeaderBag::getDate()`, `Response::getDate()`, `getExpires()` and `getLastModified()` return a `DateTimeImmutable`
 
 HttpKernel
 ----------
 
- * `BundleInterface` no longer extends `ContainerAwareInterface`
- * Add native return types to `TraceableEventDispatcher` and to `MergeExtensionConfigurationPass`
+ * [BC break] `BundleInterface` no longer extends `ContainerAwareInterface`
+ * [BC break] Add native return types to `TraceableEventDispatcher` and to `MergeExtensionConfigurationPass`
 
 Messenger
 ---------
@@ -63,7 +100,7 @@ Messenger
 MonologBridge
 -------------
 
- * Add native return type to `Logger::clear()` and to `DebugProcessor::clear()`
+ * [BC break] Add native return type to `Logger::clear()` and to `DebugProcessor::clear()`
 
 PsrHttpMessageBridge
 --------------------
@@ -73,15 +110,15 @@ PsrHttpMessageBridge
 Routing
 -------
 
- * Add native return type to `AnnotationClassLoader::setResolver()`
+ * [BC break] Add native return type to `AnnotationClassLoader::setResolver()`
  * Deprecate Doctrine annotations support in favor of native attributes
- * Change the constructor signature of `AnnotationClassLoader` to `__construct(?string $env = null)`, passing an annotation reader as first argument is deprecated
+ * Deprecate passing an annotation reader as first argument to `AnnotationClassLoader` (new signature: `__construct(?string $env = null)`)
 
 Security
 --------
 
- * `UserValueResolver` no longer implements `ArgumentValueResolverInterface`
- * Make `PersistentToken` immutable
+ * [BC break] `UserValueResolver` no longer implements `ArgumentValueResolverInterface`
+ * [BC break] Make `PersistentToken` immutable
  * Deprecate accepting only `DateTime` for `TokenProviderInterface::updateToken()`, use `DateTimeInterface` instead
 
 Serializer
@@ -93,7 +130,7 @@ Serializer
 Templating
 ----------
 
- * The component is deprecated and will be removed in 7.0. Use Twig instead.
+ * The component is deprecated and will be removed in 7.0, use [Twig](https://twig.symfony.com) instead
 
 Validator
 ---------

UPGRADE-7.0.md

@@ -5,4 +5,5 @@ Symfony 6.4 and Symfony 7.0 will be released simultaneously at the end of Novemb
 release process, both versions will have the same features, but Symfony 7.0 won't include any deprecated features.
 To upgrade, make sure to resolve all deprecation notices.
 
-This file will be updated on the branch 7.0 for each deprecated feature that is removed.
+This file will be updated on the [7.0 branch](https://github.com/symfony/symfony/blob/7.0/UPGRADE-7.0.md) for each
+deprecated feature that is removed.