Cherry pick Swift 5.5 doc changes in AsyncSequence.swift

Author: amartini51

stdlib/public/Concurrency/AsyncSequence.swift

@@ -236,6 +236,8 @@ extension AsyncSequence {
   /// The predicate executes each time the asynchronous sequence produces an
   /// element, until either the predicate returns `false` or the sequence ends.
   ///
+  /// If the asynchronous sequence is empty, this method returns `true`.
+  ///
   /// - Parameter predicate: A closure that takes an element of the asynchronous
   ///   sequence as its argument and returns a Boolean value that indicates
   ///   whether the passed element satisfies a condition.