update FullyQualifiedName

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Primitives/CSharpType.cs

@@ -105,7 +105,6 @@ public CSharpType(Type type, IReadOnlyList<CSharpType> arguments, bool isNullabl
             Name = type.IsGenericType ? type.Name.Substring(0, type.Name.IndexOf('`')) : type.Name;
             IsValueType = type.IsValueType;
             Namespace = type.Namespace ?? string.Empty;
-            FullyQualifiedName = $"{Namespace}.{Name}";
             IsPublic = type.IsPublic && arguments.All(t => t.IsPublic);
             // open generic parameter such as the `T` in `List<T>` is considered as declared inside the `List<T>` type as well, but we just want this to be the pure nested type, therefore here we exclude the open generic parameter scenario
             // for a closed generic parameter such as the `string` in `List<string>`, it is just an ordinary type without a `DeclaringType`.
@@ -153,7 +152,6 @@ internal CSharpType(
             IsValueType = isValueType;
             IsNullable = isNullable;
             Namespace = ns;
-            FullyQualifiedName = $"{ns}.{name}";
             DeclaringType = declaringType;
             IsPublic = isPublic;
             IsStruct = isStruct;
@@ -167,7 +165,7 @@ internal CSharpType(
         /// Gets or sets the name of the type.
         /// </summary>
         public string Name { get; private set; }
-        internal string FullyQualifiedName { get; private set; }
+        internal string FullyQualifiedName => $"{Namespace}.{Name}";
         public CSharpType? DeclaringType { get; private init; }
         public bool IsValueType { get; private init; }
         public bool IsEnum => _underlyingType is not null;
@@ -660,12 +658,10 @@ public void Update(string? name = null, string? @namespace = null)
             if (name != null)
             {
                 Name = name;
-                FullyQualifiedName = $"{Namespace}.{name}";
             }
             if (@namespace != null)
             {
                 Namespace = @namespace;
-                FullyQualifiedName = $"{@namespace}.{name}";
             }
         }
     }