feat: Experimental WASM Extensions

[jwerle]

This PR introduces support for WASM C/C++ extensions that support a subset of libc and the Socket Runtime Native Extension API.

Targeting wasm32 extensions is experimental as the ABI and APIs may be incomplete or subject to change

WASM extensions can be configured like:

[meta]
name = "my-wasm-extension"
type = "extension"

[extension]
target = "wasm32"
sources[] = extension.cc

Implemented like:

#include <socket/extension.h>
#include <string.h>

static void onEcho (
  sapi_context_t* context,
  sapi_ipc_message_t* message,
  const sapi_ipc_router_t* router
) {
  auto result = sapi_ipc_result_create(context, message);
  auto value = sapi_ipc_mesage_get(message, "value");
  auto data = sapi_json_string_create(context, value);
  sapi_ipc_result_set_json_data(result, sapi_json_any(data));
  sapi_ipc_reply(result);
}

static bool initialize (sapi_context_t* context, const void* data) {
  sapi_ipc_router_map(context, "my-wasm-extension.echo", onEcho, NULL);
  return true;
}

SOCKET_RUNTIME_REGISTER_EXTENSION("my-wasm-extension", initialize);

Consumed like this:

import extension from 'socket:extension'

const wasm = await extension.load('my-wasm-extension')
const result = await wasm.binding.echo({ value: 'hello' })
console.log(result.data) // 'hello'

[chicoxyzzy]

macOS CI is failing with

error: unable to create target: 'No available targets are compatible with triple "wasm32"'