Fix shimmed implementation of TryGetHashAndReset to handle HMAC.

The TryGetHashAndReset switches on the algorithm name of IncrementalHash. IncrementalHash prepends "HMAC" in front of the algorithm name, so the shim did not correctly handle the HMAC-prepended algorithm names.

This gets rid of the switch, since it was only used as an optimization in a non-success path.

Author: vcsjones

src/libraries/Microsoft.Bcl.Cryptography/src/System/Security/Cryptography/NetStandardShims.cs

@@ -100,25 +100,14 @@ internal static bool TryGetHashAndReset(
             Span<byte> destination,
             out int bytesWritten)
         {
-            int hashSize = hash.AlgorithmName.Name switch
-            {
-                nameof(HashAlgorithmName.MD5) => 128 >> 3,
-                nameof(HashAlgorithmName.SHA1) => 160 >> 3,
-                nameof(HashAlgorithmName.SHA256) => 256 >> 3,
-                nameof(HashAlgorithmName.SHA384) => 384 >> 3,
-                nameof(HashAlgorithmName.SHA512) => 512 >> 3,
-                _ => throw new CryptographicException(),
-            };
-
-            if (destination.Length < hashSize)
+            byte[] actual = hash.GetHashAndReset();
+
+            if (destination.Length < actual.Length)
             {
                 bytesWritten = 0;
                 return false;
             }
 
-            byte[] actual = hash.GetHashAndReset();
-            Debug.Assert(actual.Length == hashSize);
-
             actual.AsSpan().CopyTo(destination);
             bytesWritten = actual.Length;
             return true;