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

Comienza por mapear el puente existente entre JavaScript y WASM y los puntos de entrada indicados: swjs_core, swjs_object, swjs_string, swjs_function y swjs_typedarray. Determina el límite de la API pública del plugin y cómo podrían utilizarla las funcionalidades de JavaScriptKit indicadas; se considera terminado cuando el diseño está establecido y las funciones propuestas pueden migrarse sin añadir funcionalidad no utilizada a cada bundle.