Move the typeParameterList cast to its own function

Instead of repeating the cast for each version of BuildStandardTextSyntaxList
I moved the typeParameterList cast to its own function

Author: tokarzkj

StyleCop.Analyzers/StyleCop.Analyzers.CodeFixes/DocumentationRules/SA1642SA1643CodeFixProvider.cs

@@ -119,15 +119,7 @@ internal static ImmutableArray<string> GenerateStandardText(Document document, B
 
         internal static SyntaxList<XmlNodeSyntax> BuildStandardTextSyntaxList(BaseTypeDeclarationSyntax typeDeclaration, string preText, string postText)
         {
-            TypeParameterListSyntax typeParameterList;
-            if (typeDeclaration is ClassDeclarationSyntax classDeclaration)
-            {
-                typeParameterList = classDeclaration.TypeParameterList;
-            }
-            else
-            {
-                typeParameterList = (typeDeclaration as StructDeclarationSyntax)?.TypeParameterList;
-            }
+            TypeParameterListSyntax typeParameterList = GetTypeParameterList(typeDeclaration);
 
             return XmlSyntaxFactory.List(
                 XmlSyntaxFactory.Text(preText),
@@ -137,15 +129,7 @@ internal static SyntaxList<XmlNodeSyntax> BuildStandardTextSyntaxList(BaseTypeDe
 
         internal static SyntaxList<XmlNodeSyntax> BuildStandardTextSyntaxList(BaseTypeDeclarationSyntax typeDeclaration, string newLineText, string preText, string postText)
         {
-            TypeParameterListSyntax typeParameterList;
-            if (typeDeclaration is ClassDeclarationSyntax classDeclaration)
-            {
-                typeParameterList = classDeclaration.TypeParameterList;
-            }
-            else
-            {
-                typeParameterList = (typeDeclaration as StructDeclarationSyntax)?.TypeParameterList;
-            }
+            TypeParameterListSyntax typeParameterList = GetTypeParameterList(typeDeclaration);
 
             return XmlSyntaxFactory.List(
                 XmlSyntaxFactory.NewLine(newLineText),
@@ -154,6 +138,16 @@ internal static SyntaxList<XmlNodeSyntax> BuildStandardTextSyntaxList(BaseTypeDe
                 XmlSyntaxFactory.Text(postText.EndsWith(".") ? postText : (postText + ".")));
         }
 
+        private static TypeParameterListSyntax GetTypeParameterList(BaseTypeDeclarationSyntax typeDeclaration)
+        {
+            if (typeDeclaration is ClassDeclarationSyntax classDeclaration)
+            {
+                return classDeclaration.TypeParameterList;
+            }
+
+            return (typeDeclaration as StructDeclarationSyntax)?.TypeParameterList;
+        }
+
         private static Task<Document> GetTransformedDocumentAsync(Document document, SyntaxNode root, XmlElementSyntax node, CancellationToken cancellationToken)
         {
             var typeDeclaration = node.FirstAncestorOrSelf<BaseTypeDeclarationSyntax>();