add range_slider

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

         }
     }
     
-    public delegate Thumb RangeThumbSelector(TextDirection textDirection,
+    public delegate Thumb? RangeThumbSelector(TextDirection textDirection,
-    double tapValue,
+    float tapValue,
     Size thumbSize,
     Size trackSize,
     float dx