Deprecate redundant EdmDeltaResourceObject and EdmDeltaComplexObject

Originally, EdmStructuredObject (the base class for EdmEntityObject and EdmComplexObject) did not implement IEdmChangedObject. However, four years ago, a change was introduced through [this commit](https://github.com/OData/AspNetCoreOData/commit/ee937986a197b9a231f63017790b3cfd3ce0621b) to make EdmStructuredObject implement IEdmChangedObject. This allowed both EdmEntityObject and EdmComplexObject to represent delta payloads.

As a result, EdmDeltaResourceObject and EdmDeltaComplexObject became redundant and should have been deprecated, as noted in this TODO:
[EdmDeltaResourceObject.cs#L24](https://github.com/OData/AspNetCoreOData/blame/c60d9e0e9f68d23ee8ccd84e854ef7e430fe6edb/src/Microsoft.AspNetCore.OData/Formatter/Value/EdmDeltaResourceObject.cs#L24)

I think we should mark redundant EdmDeltaResourceObject and EdmDeltaComplexObject as obsolete and remove them in the next major release

Start with the TODO in EdmDeltaResourceObject.cs and inspect the corresponding EdmDeltaComplexObject implementation, then compare both with EdmStructuredObject and IEdmChangedObject. Confirm the obsolete-marking and next-major-release expectations; done means the redundant types are handled consistently without breaking the current release.