Plugin infrastructure

Currently, JavaScript-based features must be directly implemented in JavaScriptKit to be able to access important features like the heap and the JSValue parsing/serializing routines. This means that less-common things like TypedArray or potential Combine-Promise integration (see #62) would have to increase the bundle size for everyone. One solution to this would be defining some sort of public JS-side API that allows providing custom functions to the WASM runtime. As long as we encourage users of this API to prefix their methods there should be no collision issues.

It would be nice to restructure JavaScriptKit itself to make use of the plugin API too:

• swjs_core: release
• swjs_object: get_prop, set_prop, get_subscript, set_subscript, instanceof
• swjs_string: decode, encode, load
• swjs_function: call, apply, call_new, create
• swjs_typedarray: create

まず、既存の JavaScript/WASM ブリッジと、一覧にあるエントリポイント swjs_core、swjs_object、swjs_string、swjs_function、swjs_typedarray をマッピングします。公開 Plugin API の境界と、一覧にある JavaScriptKit の機能がそれをどのように利用できるかを明確にします。完了とは、設計が確定し、すべての bundle に未使用の機能を追加することなく、提案された関数を移行できる状態です。