refactor(Storage): Deprecate UploadValidationException

Mark UploadValidationException as [Obsolete] to signal the transition
from client-side to server-side upload validation.

Server-side validation now returns a GoogleApiException with a
400 (Bad Request) status code instead of throwing this custom exception.
This change maintains binary compatibility while providing a migration
path for existing catch blocks.

Author: mahendra-google

apis/Google.Cloud.Storage.V1/Google.Cloud.Storage.V1.Tests/UploadValidationExceptionTest.cs

@@ -1,4 +1,4 @@
-// Copyright 2017 Google Inc. All Rights Reserved.
+// Copyright 2017 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -21,13 +21,15 @@ namespace Google.Cloud.Storage.V1.Tests
     public class UploadValidationExceptionTest
     {
         [Fact]
+        [Obsolete]
         public void Construction_NoAdditionalFailure()
         {
             var ex = new UploadValidationException("hash", new Object(), null);
             Assert.Null(ex.AdditionalFailures);
         }
 
         [Fact]
+        [Obsolete]
         public void Construction_WithAdditionalFailure()
         {
             var additional = new Exception();
@@ -36,6 +38,7 @@ public void Construction_WithAdditionalFailure()
         }
 
         [Fact]
+        [Obsolete]
         public void Construction_WithAdditionalFailure_Empty()
         {
             Assert.Throws<ArgumentException>(() => new UploadValidationException("hash", new Object(), new AggregateException("No inner exceptions")));

apis/Google.Cloud.Storage.V1/Google.Cloud.Storage.V1/StorageClientImpl.UploadObject.cs

@@ -195,7 +195,6 @@ internal Object Execute()
                     {
                         additionalFailures = new AggregateException(e);
                     }
-                    throw new UploadValidationException(hash, result, additionalFailures);
                 }
                 return result;
             }
@@ -220,7 +219,6 @@ internal async Task<Object> ExecuteAsync(CancellationToken cancellationToken)
                     {
                         additionalFailures = new AggregateException(e);
                     }
-                    throw new UploadValidationException(hash, result, additionalFailures);
                 }
                 return result;
             }

apis/Google.Cloud.Storage.V1/Google.Cloud.Storage.V1/UploadValidationException.cs

@@ -1,4 +1,4 @@
-// Copyright 2017 Google Inc. All Rights Reserved.
+// Copyright 2017 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -22,6 +22,8 @@ namespace Google.Cloud.Storage.V1
     /// <summary>
     /// Exception thrown when an upload failed validation.
     /// </summary>
+    [Obsolete("This exception is no longer thrown. Server-side validation is now performed, " +
+              "resulting in a GoogleApiException with a 400 (Bad Request) status code on failure.")]
     public sealed class UploadValidationException : IOException
     {
         /// <summary>