fix move to next page in paged response

[gearama]

closes #5617

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[antkmsft]

FWIW, here is what code our current codegen would generate for pageable:

• hpp: https://github.com/Azure/autorest.cpp/blob/next/packages/typespec-cpp/test/cadl-ranch/http/payload/pageable/generated/inc/payload/pageable/rest_client.hpp
• cpp: https://github.com/Azure/autorest.cpp/blob/next/packages/typespec-cpp/test/cadl-ranch/http/payload/pageable/generated/src/rest_client.cpp

I didn't find a private constructor there, but the codegen is essentially doing the same by doing this:

  ListPagedResponse response{};
  response.m_client = std::make_shared<PageableClient>(*this);
  response.m_options = options;

I am not proposing that you necessarily should remove the constructor, but I am more making an argument for the construction being private.