Add missing <returns> documentation to NonCryptographicHashAlgorithm

Author: bartonjs

src/libraries/System.IO.Hashing/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs

@@ -133,6 +133,9 @@ public void Append(Stream stream)
         ///   The token to monitor for cancellation requests.
         ///   The default value is <see cref="CancellationToken.None"/>.
         /// </param>
+        /// <returns>
+        ///   A task that represents the asynchronous append operation.
+        /// </returns>
         /// <exception cref="ArgumentNullException">
         ///   <paramref name="stream"/> is <see langword="null"/>.
         /// </exception>
@@ -172,6 +175,9 @@ private async Task AppendAsyncCore(Stream stream, CancellationToken cancellation
         /// <summary>
         ///   Gets the current computed hash value without modifying accumulated state.
         /// </summary>
+        /// <returns>
+        ///   The hash value for the data already provided.
+        /// </returns>
         public byte[] GetCurrentHash()
         {
             byte[] ret = new byte[HashLengthInBytes];
@@ -230,6 +236,9 @@ public int GetCurrentHash(Span<byte> destination)
         /// <summary>
         ///   Gets the current computed hash value and clears the accumulated state.
         /// </summary>
+        /// <returns>
+        ///   The hash value for the data already provided.
+        /// </returns>
         public byte[] GetHashAndReset()
         {
             byte[] ret = new byte[HashLengthInBytes];