[Symfony 6] Add "array|string|int|float|bool|\ArrayObject|null" to all Normalizer classes that implement the method ::normalize()

Problem/Motivation

Method "Symfony\Component\Serializer\Normalizer\NormalizerInterface::normalize()" will return "array|string|int|float|bool|\ArrayObject|null" as of its next major version.

This deprecation warning is given by Symfony 5.4 that in Symfony 6 the return value must be of the type: array|string|int|float|bool|\ArrayObject|null.

In #3232074: [Symfony 6] Add "array|string|int|float|bool|\ArrayObject|null" to all Normalizer classes that implement the method ::normalize() we fixed CacheableNormalizations as they are not one of the listed types, but we did not resolve the deprecation warnings.

Proposed resolution

Remaining tasks

User interface changes

None

API changes

None

Data model changes

None

Release notes snippet