[Notifier] Add more specific types at documentation level when php engine can't

src/Symfony/Component/Notifier/Bridge/Nexmo/NexmoTransportFactory.php

@@ -23,6 +23,9 @@ use Symfony\Component\Notifier\Transport\TransportInterface;
  */
 final class NexmoTransportFactory extends AbstractTransportFactory
 {
+    /**
+     * @return NexmoTransport
+     */
     public function create(Dsn $dsn): TransportInterface
     {
         $scheme = $dsn->getScheme();

src/Symfony/Component/Notifier/Bridge/Slack/SlackTransportFactory.php

@@ -23,6 +23,9 @@ use Symfony\Component\Notifier\Transport\TransportInterface;
  */
 final class SlackTransportFactory extends AbstractTransportFactory
 {
+    /**
+     * @return SlackTransport
+     */
     public function create(Dsn $dsn): TransportInterface
     {
         $scheme = $dsn->getScheme();

src/Symfony/Component/Notifier/Bridge/Telegram/TelegramTransportFactory.php

@@ -24,6 +24,9 @@ use Symfony\Component\Notifier\Transport\TransportInterface;
  */
 final class TelegramTransportFactory extends AbstractTransportFactory
 {
+    /**
+     * @return TelegramTransport
+     */
     public function create(Dsn $dsn): TransportInterface
     {
         $scheme = $dsn->getScheme();

src/Symfony/Component/Notifier/Bridge/Twilio/TwilioTransportFactory.php

@@ -23,6 +23,9 @@ use Symfony\Component\Notifier\Transport\TransportInterface;
  */
 final class TwilioTransportFactory extends AbstractTransportFactory
 {
+    /**
+     * @return TwilioTransport
+     */
     public function create(Dsn $dsn): TransportInterface
     {
         $scheme = $dsn->getScheme();

src/Symfony/Component/Notifier/Message/SmsMessage.php

@@ -58,7 +58,7 @@ final class SmsMessage implements MessageInterface
         return $this->phone;
     }
 
-    public function getRecipientId(): ?string
+    public function getRecipientId(): string
     {
         return $this->phone;
     }

src/Symfony/Component/Notifier/Transport/NullTransportFactory.php

@@ -20,6 +20,9 @@ use Symfony\Component\Notifier\Exception\UnsupportedSchemeException;
  */
 final class NullTransportFactory extends AbstractTransportFactory
 {
+    /**
+     * @return NullTransport
+     */
     public function create(Dsn $dsn): TransportInterface
     {
         if ('null' === $dsn->getScheme()) {