[Symfony 6] Add various type hints to Drupal\serialization\Encoder\JsonEncoder::supportsEncoding() and ::supportsDecoding() and Drupal\serialization\Encoder\XmlEncoder::supportsEncoding(), ::encode(), ::decode() and ::supportsDecoding()

Problem/Motivation

Method "Symfony\Component\Serializer\Encoder\EncoderInterface::supportsEncoding()" will return "bool" as of its next major version. Doing the same in implementation "Drupal\serialization\Encoder\JsonEncoder" will be required when upgrading.

Method "Symfony\Component\Serializer\Encoder\DecoderInterface::supportsDecoding()" will return "bool" as of its next major version. Doing the same in implementation "Drupal\serialization\Encoder\JsonEncoder" will be required when upgrading.

Method "Symfony\Component\Serializer\Encoder\EncoderInterface::encode()" will return "string" as of its next major version. Doing the same in implementation "Drupal\serialization\Encoder\XmlEncoder" will be required when upgrading.

Method "Symfony\Component\Serializer\Encoder\EncoderInterface::supportsEncoding()" will return "bool" as of its next major version. Doing the same in implementation "Drupal\serialization\Encoder\XmlEncoder" will be required when upgrading.

Method "Symfony\Component\Serializer\Encoder\DecoderInterface::decode()" will return "mixed" as of its next major version. Doing the same in implementation "Drupal\serialization\Encoder\XmlEncoder" will be required when upgrading.

Method "Symfony\Component\Serializer\Encoder\DecoderInterface::supportsDecoding()" will return "bool" as of its next major version. Doing the same in implementation "Drupal\serialization\Encoder\XmlEncoder" will be required when upgrading.

Steps to reproduce

Proposed resolution

Add the various return type hints.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet