Simplify code.

src/Features/Core/Portable/GenerateConstructorFromMembers/FieldDelegatingCodeAction.cs

@@ -78,7 +78,7 @@ protected override async Task<Document> GetChangedDocumentAsync(CancellationToke
                 var result = await CodeGenerator.AddMemberDeclarationsAsync(
                     _document.Project.Solution,
                     _state.ContainingType,
-                    fields.Cast<ISymbol>().Concat(constructor),
+                    fields.Concat(constructor),
                     new CodeGenerationOptions(
                         contextLocation: syntaxTree.GetLocation(_state.TextSpan),
                         afterThisLocation: afterThisLocation),

src/Features/Core/Portable/GenerateMember/GenerateConstructor/AbstractGenerateConstructorService.Editor.cs

@@ -219,7 +219,7 @@ private async Task<(Document, bool addedFields)> GenerateFieldDelegatingConstruc
                 var result = await codeGenerationService.AddMembersAsync(
                     _document.Project.Solution,
                     _state.TypeToGenerateIn,
-                    fields.Cast<ISymbol>().Concat(constructor),
+                    fields.Concat(constructor),
                     new CodeGenerationOptions(_state.Token.GetLocation()),
                     _cancellationToken)
                     .ConfigureAwait(false);

src/Workspaces/Core/Portable/Shared/Extensions/ICodeDefinitionFactoryExtensions.cs

@@ -63,7 +63,7 @@ internal static partial class ICodeDefinitionFactoryExtensions
                     : factory.CreateArguments(constructor.Parameters));
         }
 
-        public static (ImmutableArray<IFieldSymbol> fields, IMethodSymbol constructor) CreateFieldDelegatingConstructor(
+        public static (ImmutableArray<ISymbol> fields, ISymbol constructor) CreateFieldDelegatingConstructor(
             this SyntaxGenerator factory,
             Compilation compilation,
             string typeName,
@@ -90,7 +90,7 @@ internal static partial class ICodeDefinitionFactoryExtensions
                 statements: statements,
                 thisConstructorArguments: GetThisConstructorArguments(containingTypeOpt, parameterToExistingFieldMap));
 
-            return (fields, constructor);
+            return (ImmutableArray<ISymbol>.CastUp(fields), constructor);
         }
 
         private static ImmutableArray<SyntaxNode> GetThisConstructorArguments(