Add TaskWorklet tests

[guest271314]

TaskWorklet (see also https://github.com/developit/task-worklet) has landed in Chromium. Some tests are located at taskqueue and https://github.com/developit/task-worklet/blob/master/test/index.test.js.

The "task" type could be added to https://github.com/web-platform-tests/wpt/blob/master/worklets/resources/worklet-test-utils.js, and the corresponding tests linked above could be added to the wpt worklets directory

// Returns a reference to a worklet object corresponding to a given type.
function get_worklet(type) {
  if (type == 'animation')
    return CSS.animationWorklet;
  if (type == 'layout')
    return CSS.layoutWorklet;
  if (type == 'paint')
    return CSS.paintWorklet;
  if (type == 'audio')
    return new OfflineAudioContext(2,44100*40,44100).audioWorklet;
 if (type == 'task') // add `"task"` type to wpt test
    return taskWorklet;
  return undefined;
}