[TCGC] Add a flag to indicate an SdkMethod is overloaded or not

[haolingdong-msft]

I understad there are many things not decided about operation overload. So I would like to limit the scope of this issue to add flag (e.g. called isOverloadedOperation) to indicate if an SdkMethodh has @overloaded decorator.

Java emitter currently checks if the operation is overloaded or not by checking if the operation has @overload decorator, this will be used to generate protocol method only for overloaded operation. See code: https://github.com/Azure/autorest.java/blob/main/typespec-extension/src/code-model-builder.ts#L706-L714

[tadelesh]

close since we decide not to support @overload.