[Concurrency] Initial TaskGroup implementation working

Author: ktoso

docs/SIL.rst

@@ -656,7 +656,7 @@ the coroutine until the continuation is invoked to resume it.  A use of
 
   func waitForCallback() async -> Int {
     return await withUnsafeContinuation { cc in
-      registerCallback { cc.resume(returning: $0) }
+      registerCallback { cc.resume($0) }
     }
   }
 

include/swift/ABI/MetadataValues.h

@@ -1925,15 +1925,9 @@ class JobFlags : public FlagSet<size_t> {
 
     // Kind-specific flags.
 
-    Task_IsChildTask      = 24,
-    Task_IsFuture         = 25,
-    // A TaskGroup is a Channel Task which allows children to offer values into
-    // it as they complete
-    Task_IsChannel        = 26,
-    // A child task started in a TaskGroup.
-    // Its parent MUST be the group's channel task,
-    // and the child task MUST offer its completion value into it when it completes.
-    Task_IsGroupChild     = 27,
+    Task_IsChildTask  = 24,
+    Task_IsFuture     = 25,
+    Task_IsTaskGroup  = 26,
   };
 
   explicit JobFlags(size_t bits) : FlagSet(bits) {}
@@ -1961,12 +1955,9 @@ class JobFlags : public FlagSet<size_t> {
                                 task_isFuture,
                                 task_setIsFuture)
 
-  FLAGSET_DEFINE_FLAG_ACCESSORS(Task_IsChannel,
-                                task_isChannel,
-                                task_setIsChannel)
-  FLAGSET_DEFINE_FLAG_ACCESSORS(Task_IsGroupChild,
-                                task_isGroupChild,
-                                task_setGroupChild)
+  FLAGSET_DEFINE_FLAG_ACCESSORS(Task_IsTaskGroup,
+                                task_isTaskGroup,
+                                task_setIsTaskGroup)
 
 };