Add ReferenceHandler to JsonSourceGenerationOptions

[PranavSenthilnathan]

Adds a ReferenceHandler property to JsonSourceGenerationOptions to allow users to specify how references are handled when generating source code for JSON types.

Implements #107597

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This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

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[eiriktsarpalis]

Not saying that this wouldn't work, but ReferenceHandler isn't technically an enum. It's a class with static properties, so perhaps different concerns apply to formatting it?

[PranavSenthilnathan]

The default value of the enum didn't map to a default reference handler in the first iteration of this PR. Updated the PR to handle this enum -> reference handler object conversion. Note that for the naming policy, we actually have the policy classes in the Common folder so nameof works there. I tried to see if I could also move ReferenceHandler to Common but it has a couple of dependencies so I just left it as it is instead of adding a bunch of types to Common. I just hardcoded the property names for this PR.

[eiriktsarpalis]

Left some feedback, but this looks great so far 👍

[eiriktsarpalis]

Thanks!