Fix runOnJS on Web and make it asynchronous

[tjzel]

Summary

This PR is amending some changes from #4276 where we exchanged setImmediates for queueMicrotask for _scheduneOnJS.

queueMicrotask does not take any arguments, only a callback and the change of behaviour stemming from this was not considered in runOnJS implementation. This PR fixes this and also makes runOnJS actually call _scheduleOnJS on web, making it asynchronous and consistent with general behavior of runOnJS - before it was unreachable code on web since it would simply return the provided function that was called synchronously.

Test plan

Run WebExample and see that now runOnJS is working properly. I used the following snippet:

function foo() {
    console.log('hello');
  }

  function foz(str: string) {
    console.log(str);
  }

  runOnJS(foo)();
  runOnJS(foz)('bye');

  function bar() {
    console.log('hello again');
  }

  function baz(str: string) {
    console.log(str);
  }

  runOnUI(() => {
    runOnJS(bar)();
    runOnJS(baz)('bye again');
  })();

Before:

After: