Serialization is not repeatable

[fcool]

Description

DependencyInjection build by the \Neos\Flow\ObjectManagement\DependencyInjection\ProxyClassBuilder leads to unrepeatable serialization.
In the second call all related entities are lost in the serialized form.
This espacially happens if you use an object in some kind of deferred workflow (for example using the functionality of Flowpack.JobQueue.Common and having the same object in a session, where it gets serialized again)
Those errors are tremendous hard to debug, as its only missing in the serialized form, so it will cause trouble in the disconnected process, which uses unserialize - and now misses all related data. As session savement is done after the response is done it gets worse, as there is no possibility to tell the user, that something gone wrong.

Steps to Reproduce

(See the provided test case #2010)

1. Create an object having a property with an already persisted entity
2. serialize it twice
3. unserialize the second serializedData

Expected behavior

I expect serialize($object) to be repeatable without leading to different results

Affected Versions

Flow: 4.3 - 6.2

[fcool]

Let me know, if I should retarget for version 5.3. As the change is mergeable in all majors I targeted 4.3 as problems in serialization often leads to quite unexpected attac vectors.

[sorenmalling]

@albe This issue can be closed now thanks your merging?