Expose a platform detection mechanism

It would be great if `componentize-js` (or possibly one level lower at StarlingMonkey) could expose a platform detection mechanism JS that is used for components to rely upon. This would enable building "isomorphic" codebases that could work in wasm as well as non-wasm environments, assuming that builds were properly set up to *produce* such JS projects.

首先追蹤 componentize-js 與 StarlingMonkey 之間提出的整合邊界，因為 issue 尚未確定實作層級。定義平台偵測 JavaScript 介面，並驗證元件能在 wasm 和 non-wasm 建置中使用該介面；當一個已公開的機制支援這些同構專案時，即視為完成。

由索引模型根據 Issue 內容生成。