Add tsan_release edge on task creation

without this, we are getting false data races between when a task
is created and immediately scheduled on a different thread.

False positive for `Sanitizers/tsan/actor_counters.swift` test:
```
WARNING: ThreadSanitizer: data race (pid=81452)
  Read of size 8 at 0x7b2000000560 by thread T5:
    #0 Counter.next() <null>:2 (a.out:x86_64+0x1000047f8)
    #1 (1) suspend resume partial function for worker(identity:counters:numIterations:) <null>:2 (a.out:x86_64+0x100005961)
    #2 swift::runJobInEstablishedExecutorContext(swift::Job*) <null>:2 (libswift_Concurrency.dylib:x86_64+0x280ef)

  Previous write of size 8 at 0x7b2000000560 by main thread:
    #0 Counter.init(maxCount:) <null>:2 (a.out:x86_64+0x1000046af)
    #1 Counter.__allocating_init(maxCount:) <null>:2 (a.out:x86_64+0x100004619)
    #2 runTest(numCounters:numWorkers:numIterations:) <null>:2 (a.out:x86_64+0x100006d2e)
    #3 swift::runJobInEstablishedExecutorContext(swift::Job*) <null>:2 (libswift_Concurrency.dylib:x86_64+0x280ef)
    #4 main <null>:2 (a.out:x86_64+0x10000a175)
```

New edge with this change:
```
[4357150208] allocate task 0x7b3800000000, parent = 0x0
[4357150208] creating task 0x7b3800000000 with parent 0x0
[4357150208] tsan_release on 0x7b3800000000    <<< new release edge
[139088221442048] tsan_acquire on 0x7b3800000000
[139088221442048] trying to switch from executor 0x0 to 0x7ff85e2d9a00
[139088221442048] switch failed, task 0x7b3800000000 enqueued on executor 0x7ff85e2d9a00
[139088221442048] enqueue job 0x7b3800000000 on executor 0x7ff85e2d9a00
[139088221442048] tsan_release on 0x7b3800000000
[139088221442048] tsan_release on 0x7b3800000000
[4357150208] tsan_acquire on 0x7b3800000000
counters: 1, workers: 1, iterations: 1
[4357150208] allocate task 0x7b3c00000000, parent = 0x0
[4357150208] creating task 0x7b3c00000000 with parent 0x0
[4357150208] tsan_release on 0x7b3c00000000    <<< new release edge
[139088221442048] tsan_acquire on 0x7b3c00000000
[4357150208] task 0x7b3800000000 waiting on task 0x7b3c00000000, going to sleep
[4357150208] tsan_release on 0x7b3800000000
[4357150208] tsan_release on 0x7b3800000000
[139088221442048] getting current executor 0x0
[139088221442048] tsan_release on 0x7b3c00000000
...
```

rdar://78932849

Author: Julian Lettner

stdlib/public/Concurrency/Task.cpp

@@ -582,6 +582,8 @@ static AsyncTaskAndContext swift_task_create_group_future_commonImpl(
   initialContext->Flags = AsyncContextKind::Ordinary;
   initialContext->Flags.setShouldNotDeallocateInCallee(true);
 
+  _swift_tsan_release(task);
+
   return {task, initialContext};
 }