Report error when MetadataUpdateDeletedAttribute is applied manually (#80125)

Author: tmat

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -8196,4 +8196,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
     <value>'MethodImplAttribute.Async' cannot be manually applied to methods. Mark the method 'async'.</value>
     <remarks>'MethodImplAttribute.Async' and 'async' are not localizable.</remarks>
   </data>
+  <data name="ERR_AttributeCannotBeAppliedManually" xml:space="preserve">
+    <value>'{0}' cannot be applied manually.</value>
+  </data>
 </root>

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -2425,6 +2425,7 @@ internal enum ErrorCode
         ERR_UnsupportedFeatureInRuntimeAsync = 9328,
         ERR_ExtensionBlockCollision = 9329,
         ERR_MethodImplAttributeAsyncCannotBeUsed = 9330,
+        ERR_AttributeCannotBeAppliedManually = 9331,
 
         // Note: you will need to do the following after adding errors:
         //  1) Update ErrorFacts.IsBuildOnlyDiagnostic (src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs)

src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs

@@ -2536,6 +2536,7 @@ or ErrorCode.ERR_MemberNameSameAsExtendedType
                 or ErrorCode.ERR_FeatureNotAvailableInVersion14
                 or ErrorCode.ERR_ExtensionBlockCollision
                 or ErrorCode.ERR_MethodImplAttributeAsyncCannotBeUsed
+                or ErrorCode.ERR_AttributeCannotBeAppliedManually
                     => false,
             };
 #pragma warning restore CS8524 // The switch expression does not handle some values of its input type (it is not exhaustive) involving an unnamed enum value.

src/Compilers/CSharp/Portable/Symbols/Symbol_Attributes.cs

@@ -230,6 +230,10 @@ protected void DecodeWellKnownAttribute(ref DecodeWellKnownAttributeArguments<At
                     arguments.Diagnostics.DiagnosticBag.Add(ErrorCode.ERR_InvalidExperimentalDiagID, attrArgumentLocation);
                 }
             }
+            else if (arguments.Attribute.IsTargetAttribute(AttributeDescription.MetadataUpdateDeletedAttribute))
+            {
+                arguments.Diagnostics.DiagnosticBag.Add(ErrorCode.ERR_AttributeCannotBeAppliedManually, arguments.AttributeSyntaxOpt!.Location, args: [AttributeDescription.MetadataUpdateDeletedAttribute.FullName]);
+            }
 
             DecodeWellKnownAttributeImpl(ref arguments);
         }