[EnC] Make it a rude edit to change the value of a constant field

src/Features/CSharp/EditAndContinue/CSharpEditAndContinueAnalyzer.cs

@@ -2110,8 +2110,8 @@ private void ClassifyUpdate(VariableDeclaratorSyntax oldNode, VariableDeclarator
                 }
 
                 // Check if a constant field is updated:
-                var fieldDeclaration = oldNode.Parent.Parent as FieldDeclarationSyntax;
-                if (fieldDeclaration != null && fieldDeclaration.Modifiers.Any(SyntaxKind.ConstKeyword))
+                var fieldDeclaration = (FieldDeclarationSyntax)oldNode.Parent.Parent;
+                if (fieldDeclaration.Modifiers.Any(SyntaxKind.ConstKeyword))
                 {
                     ReportError(RudeEditKind.Update);
                     return;

src/Features/VisualBasic/EditAndContinue/VisualBasicEditAndContinueAnalyzer.vb

@@ -2275,8 +2275,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.EditAndContinue
                                                   newNode.Initializer,
                                                   newNode.AsClause) Then
                     ' Check if a constant field is updated:
-                    Dim fieldDeclaration = TryCast(oldNode.Parent, FieldDeclarationSyntax)
-                    If fieldDeclaration IsNot Nothing AndAlso fieldDeclaration.Modifiers.Any(SyntaxKind.ConstKeyword) Then
+                    Dim fieldDeclaration = DirectCast(oldNode.Parent, FieldDeclarationSyntax)
+                    If fieldDeclaration.Modifiers.Any(SyntaxKind.ConstKeyword) Then
                         ReportError(RudeEditKind.Update)
                         Return
                     End If