Use serializedSizeZC estimate in encode_server_stream
Use serializedSizeZC estimate in encode_server_stream

Summary:
1. We do this for pretty much all other Thrift serialization in generated code, e.g., for request/response on client/server.
2. Streaming servers tend to be memory-sensitive. Moreover, when using the publisher API, it is possible for the server to accumulate many serialized payloads in memory. Using serializedSizeZC can help this situation.
3. Some streaming servers send back huge payloads, but many stream responses are tiny, where 4kb is way overkill.

Reviewed By: yfeldblum, rhodo

Differential Revision: D22165911

fbshipit-source-id: 040f970667132a28d65a3bf1e7f7318439eed804

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