enhance: only show syntax-highlighting toggle if current revision content is a text file

Signed-off-by: leo <longshuang@msn.cn>

src/Converters/ObjectConverters.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Globalization;
+using Avalonia.Data.Converters;
+
+namespace SourceGit.Converters
+{
+    public static class ObjectConverters
+    {
+        public class IsTypeOfConverter : IValueConverter
+        {
+            public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+            {
+                if (value == null || parameter == null)
+                    return false;
+
+                return value.GetType().IsAssignableTo((Type)parameter);
+            }
+
+            public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+            {
+                return new NotImplementedException();
+            }
+        }
+
+        public static readonly IsTypeOfConverter IsTypeOf = new IsTypeOfConverter();
+    }
+}