[UUF] No polymorphic classes in this article

### Type of issue

Other (describe below)

### Description

"There are no polymorphic classes in this article. So there is no serialization problem with polymorphic types. All type information completely determined on compile time. Non-virtual base class should never know about non-polymorphic inheritor's structure until we write virtual/override."

### Page URL

https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/polymorphism

### Content source URL

https://github.com/dotnet/docs/blob/main/docs/standard/serialization/system-text-json/polymorphism.md

### Document Version Independent Id

17511810-6572-ad88-6eaf-4f9bded720b7

### Article author

@gewarren

### Metadata

* ID: 179cc49a-a37d-155e-5ecf-deca4f219a5a
* Service: **dotnet-fundamentals**

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[Associated WorkItem - 286585](https://dev.azure.com/msft-skilling/Content/_workitems/edit/286585)