v2, TypeScript should not do protocol API

[weidongxu-microsoft]

v2 does not have concept of protocol/convenience API.

Emitter should not remove convenience API for v2 (on condition of e.g. multiple content-type in request, json-merge-patch).

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After we solve this, we should remove this discrepancy in code
https://github.com/microsoft/typespec/blob/main/packages/http-client-java/generator/http-client-generator/src/main/java/com/microsoft/typespec/http/client/generator/util/ModelUtil.java#L24