Added requestWrap and sendReady

[redzovic]

The user can await requestWrap until the Endpoint calls sendReady.

This is a proposed solution to the problems mentioned in #665 and #635.

It does not break the previous wrap or expose function signature but rather adds the two optional functions requestWrap() and sendReady() which can be used to avoid deadlocks.

Here is an example on how to use the proposed changes in actual code:
main.ts

import * as Comlink from "comlink";

let worker = new Worker(new URL("./extension", import.meta.url), { type: "module" });
let api = await Comlink.requestWrap(worker);

await api.hey();

extension.ts

import * as Comlink from "comlink";

Comlink.expose(
  {
    str: "exposed string",
    hey() { console.log("helloo!") },
  });

Comlink.sendReady(self);

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