Populate existing collections by default when deserializing JSON

[sebastienros]

Fixes #16585

@sarahelsaig

[sebastienros]

I found that the sessions didn't have this property. Isolated it to these defaults. I want to see if the tests still pass as we might have not set it on purpose, I remember we had issues that STJ was not able to assign new collections and we went with init setters for this reason. But I believe that if it find existing collections it will just be fine.

[MikeAlhayek]

Strange that we did not add it. I think it should be added too. I suggest that you add a test case to approve that this fixed the problem we had.

[gvkries]

This is way better than adding another JsonConverter.
Should it also be set in JsonSerializerOptionsExtensions.Merge()?

OrchardCore/src/OrchardCore/OrchardCore.Abstractions/Json/Extensions/JsonSerializerOptionsExtensions.cs

Line 10 in e23ab9e

public static JsonSerializerOptions Merge(this JsonSerializerOptions destination, JsonSerializerOptions source)

[sarahelsaig]

I agree with @gvkries , PreferredObjectCreationHandling should be added to JsonSerializerOptionsExtensions.Merge() and that should be used here instead of manually overwriting each property.
That way you will never have to manually update this configuration from JOptions.Base if a new setting is added there or something.