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.

首先跟踪 componentize-js 与 StarlingMonkey 之间提出的集成边界，因为 issue 尚未确定实现层级。定义平台检测 JavaScript 接口，并验证组件能在 wasm 和 non-wasm 构建中使用该接口；当一个已暴露的机制支持这些同构项目时，即视为完成。

由索引模型根据 Issue 内容生成。