fix(bindgen): return state-only handle when async-lowered import resolves eagerly

[andreiltd]

Per CanonicalABI.md an async-lowered import whose callee resolves synchronously returns Subtask.State.RETURNED state only and no subtask handle is packed into the result.

Separateley The CanonicalABI.md packs state into 4 bits so the check bounds are adjusted.

This the relevant spec section:

In the async case, if the callee already called on_resolve, then the RETURNED code is eagerly returned to the core wasm caller without needing to add a Subtask to the current component instance's handles table.

    if subtask.resolved():
      assert(flat_results == [])
      subtask.deliver_resolve()
      return [Subtask.State.RETURNED]
    else:
      subtaski = thread.task.inst.handles.add(subtask)
      def on_progress():
        def subtask_event():
          if subtask.resolved():
            subtask.deliver_resolve()
          return (EventCode.SUBTASK, subtaski, subtask.state)
        subtask.set_pending_event(subtask_event)
      assert(0 < subtaski <= Table.MAX_LENGTH < 2**28)
      assert(0 <= subtask.state < 2**4)
      return [subtask.state | (subtaski << 4)]

[vados-cosmonic]

LGTM 🚀

[jco-release-bot]

🎉 The code in this PR was made available in the following release:
https://github.com/bytecodealliance/jco/releases/tag/js-component-bindgen-v1.18.0