Teach TSan about TaskGroups

`TaskGroup::offer(completedTask)`:
* Called from `AsyncTask::completeFuture()` which already takes care of
  `release(completedTask)`.  No additional edge is required if no task
  is waiting and completed task is stored so it can be retrieved by
  `group.poll()`.
* If group has waiting task, it will be dequeued and scheduled, add
  `acquire(waitingTask)`.

`TaskGroupImpl::poll(waitingTask)`:
* If no pending tasks, do nothing.
* If returning finished task, `acquire(finishedTask)`.
* If enqueuing waiting task, `release(waitingTask)`.

Note: `release()` should go before, and `acquire()` after the annotated
      synchronization operation.

Radar-Id: rdar://75910632

Author: Julian Lettner

stdlib/public/Concurrency/TaskGroup.cpp

@@ -621,6 +621,8 @@ void TaskGroupImpl::offer(AsyncTask *completedTask, AsyncContext *context) {
 
         fillGroupNextResult(waitingContext, result);
 
+        _swift_tsan_acquire(static_cast<Job *>(waitingTask));
+
         // TODO: allow the caller to suggest an executor
         swift_task_enqueueGlobal(waitingTask);
         return;
@@ -750,6 +752,7 @@ PollResult TaskGroupImpl::poll(AsyncTask *waitingTask) {
           result.status = PollStatus::Success;
           result.storage = futureFragment->getStoragePtr();
           assert(result.retainedTask && "polled a task, it must be not null");
+          _swift_tsan_acquire(static_cast<Job *>(result.retainedTask));
           mutex.unlock(); // TODO: remove fragment lock, and use status for synchronization
           return result;
 
@@ -759,6 +762,7 @@ PollResult TaskGroupImpl::poll(AsyncTask *waitingTask) {
           result.storage =
               reinterpret_cast<OpaqueValue *>(futureFragment->getError());
           assert(result.retainedTask && "polled a task, it must be not null");
+          _swift_tsan_acquire(static_cast<Job *>(result.retainedTask));
           mutex.unlock(); // TODO: remove fragment lock, and use status for synchronization
           return result;
 
@@ -775,6 +779,7 @@ PollResult TaskGroupImpl::poll(AsyncTask *waitingTask) {
 
   // ==== 3) Add to wait queue -------------------------------------------------
   assert(assumed.readyTasks() == 0);
+  _swift_tsan_release(static_cast<Job *>(waitingTask));
   while (true) {
     // Put the waiting task at the beginning of the wait queue.
     if (waitQueue.compare_exchange_weak(