[RemoteMirror] Add a call for iterating over the allocations belonging to an AsyncTask.

rdar://72907056

stdlib/private/SwiftReflectionTest/SwiftReflectionTest.swift

@@ -179,6 +179,7 @@ public enum InstanceKind: UInt8 {
   case Closure
   case Enum
   case EnumValue
+  case AsyncTask
 }
 
 /// Represents a section in a loaded image in this process.
@@ -579,6 +580,12 @@ public func reflect(function: @escaping (Int, String, AnyObject?) -> Void) {
   fn.deallocate()
 }
 
+
+/// Reflect an AsyncTask.
+public func reflect(asyncTask: UInt) {
+  reflect(instanceAddress: asyncTask, kind: .AsyncTask)
+}
+
 /// Call this function to indicate to the parent that there are
 /// no more instances to look at.
 public func doneReflecting() {