client, add shadow variable for discriminator property

[weidongxu-microsoft]

another fix on #2574

Remove setKind method in superclass.
Shadow kind variable in subclass.
Override getKind method in subclass.

code change https://github.com/Azure/autorest.java/pull/2639/files/e9c1c0dbad94325dacb299fc8f29a1d6c892fd7b..db632bbb53ab4612517996b0298ea42f44824de1

test like this (for both azure-json and Jackson) e9c1c0d

[weidongxu-microsoft]

Treat polymorphic discriminator property as a property in current model.

[weidongxu-microsoft]

Here code change is just removing the condition (since we no longer skip the discriminator property).

[weidongxu-microsoft]

My origin attempt is to avoid this String type class variable, and directly provide

    @Generated
    @Override
    public String getType() {
        return "bytes";
    }

(there is a corner case on behavior difference between the 2, on a case of user directly do BinaryData("<invalid-json>").toObject(BytesData.class) with a JSON of unknown type)

But reverted to current shadow variable.
Reason is fromJson have code on either deserializedBytesData.setType(..) or deserializedBytesData.type = .., and I don't want to disrupt that part of code.

[weidongxu-microsoft]

I assume, in subclass, adding/removing the "override" of getType() in exact same method signature won't be breaking changes.

[weidongxu-microsoft]

https://revapi.org/revapi-java/0.28.1/differences.html#java.method.movedToSuperClass

"Method Moved To Superclass" is "equivalent". So I think this won't be counted as break.

[haolingdong-msft]

Just notice serialziation and deserialization part, wonder why this get removed?