minor fix

com.unity.uiwidgets/Runtime/material/text_theme.cs

 
         public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
             base.debugFillProperties(properties);
-            TextTheme defaultTheme = new Typography().black;
+            TextTheme defaultTheme = Typography.create().black;
             properties.add(new DiagnosticsProperty<TextStyle>("display4", headline1,
                 defaultValue: defaultTheme.display4));
             properties.add(new DiagnosticsProperty<TextStyle>("display3", headline2,