[C++] Investigate scalar.h usage and reduce cost of function.h include

### Describe the enhancement requested

Scalars are usually passed around via shared_ptr. So we can often get away with a forward declaration. However, clang build analyzer reports that the scalar.h header is included quite often. We should investigate why this is and see if we can shave a bit of time off our builds by fixing it.

In addition, the function.h include is rather heavy. It is included often because it is needed by the api_xyz.h files in the compute module. However, these files only need the function options. We should see if breaking function options into its own file helps shave down the build time.

### Component(s)

C++

clang build analyzerを使って、scalar.hが頻繁にインクルードされる理由を調査し、shared_ptrの使用箇所と前方宣言の機会に焦点を当てます。次に、computeモジュールのfunction.hとapi_xyz.hファイルを調べ、関数オプションを分離することでインクルードコストが削減されるかどうかを判断します。測定したビルドへの影響を文書化し、インクルード構造を適切に軽量化できれば完了です。

索引モデルが issue の本文から書いたものです。