[concurrency] stdlib: add a _runAsyncHandler compiler intrinsic.

It just calls Task.runDetatched.
It's more efficient to have a non-generic compiler intrinsic than to let the compiler call the generic Task.runDetatched.
The _runAsyncHandler doesn't have to be generic because the return value of the run function is defined to be Void.

Author: eeckstein

stdlib/public/Concurrency/Task.swift

@@ -310,6 +310,11 @@ extension Task {
 
     return Handle<T>(task: task)
   }
+
+}
+
+public func _runAsyncHandler(operation: @escaping () async -> ()) {
+  _ = Task.runDetached(operation: operation)
 }
 
 // ==== Voluntary Suspension -----------------------------------------------------