don't generate functions if there are three body types in DPG

[iscai-msft]

We don't want to generate functions with three possible input body types (i.e. send_to_all in WebPubSub) in DPG. We want to generate them as abstract methods that SDK writers have to implement. You can see how we handle formdata in DPG to see how we want to handle this.

The actual webpubsub SDK will also have to be updated to implement send_to_all (you can just copy-paste the current existing generated code), so we can pass the pipeline running on all SDKs