transcode stub

[macovedj]

This branch stubs a transcoding implementation, along with a few other changes so as to find an implementation for this issue. Building jco locally enables one to transpile the component found here, which was created by composing components found here. As described in the issue comments, the constituent components compose functions that return strings and expect strings as input values. Following this process, I found in my js bindings the following problematic code:

({ exports: exports7 } = await instantiateCore(await module8, {
    callee: {
      adapter0: exports1['hello-world'],
    },
    flags: {
      instance1: ,
      instance2: ,
    },
    memory: {
      '': exports5.memory,
    },
    post_return: {
      adapter0: exports1['cabi_post_hello-world'],
    },
    realloc: {
      '': exports5.cabi_realloc,
    },
    transcode: {
      'utf8-to-utf8 (mem0 => mem1)': ,
      'utf8-to-utf8 (mem1 => mem0)': ,
    },
  }));

Specifically, the flags and transcode fields have no values. As mentioned in this zulip thread, a createTranscoder function is probably needed for the transcode field. I don't quite know what will be needed for the flags field.

[guybedford]

Thank you @macovedj for picking this up. I've made a start in #79. Let's move the discussion there.