Change the logic for adding new task status records to a task

This change has two parts to it:

1. Add in a new interface (addStatusRecordWithChecks) for adding task
status records that also takes in a function ref. This function ref will
be used to evaluate if current state of the parent task has any changes
that need to be propagated to the child task that has been created.

This is necessary to prevent the following race between task creation
and concurrent cancellation and escalation:

a. Parent task create child task. It does lazy relaxed loads on its own
   state while doing so and propagates this state to the child.
b. Child task is created but has not been attached to the parent
   task/task group.
c. Parent task gets cancelled by another thread.
d. Child task gets linked into the parent’s task status records but no
   reevaluation has happened to account for changes that might have happened to
   the parent after (a).

2. Move status record management functions from the
Runtime/Concurrency.h to TaskPrivate.h. Remove any corresponding
overrides that are no longer needed. Remove unused tryAddStatusRecord
method whose functionality is provided by addStatusRecordWithChecks.

Radar-Id: rdar://problem/86347801

stdlib/public/Concurrency/Task.cpp

@@ -1056,19 +1056,27 @@ swift_task_addCancellationHandlerImpl(
   auto *record = new (allocation)
       CancellationNotificationStatusRecord(unsigned_handler, context);
 
-  if (swift_task_addStatusRecord(record))
-    return record;
+  bool fireHandlerNow = false;
 
-  // else, the task was already cancelled, so while the record was added,
-  // we must run it immediately here since no other task will trigger it.
-  record->run();
+  addStatusRecord(record, [&](ActiveTaskStatus parentStatus) {
+    if (parentStatus.isCancelled()) {
+      fireHandlerNow = true;
+      // We don't fire the cancellation handler here since this function needs
+      // to be idempotent
+    }
+    return true;
+  });
+
+  if (fireHandlerNow) {
+    record->run();
+  }
   return record;
 }
 
 SWIFT_CC(swift)
 static void swift_task_removeCancellationHandlerImpl(
     CancellationNotificationStatusRecord *record) {
-  swift_task_removeStatusRecord(record);
+  removeStatusRecord(record);
   swift_task_dealloc(record);
 }