add missing EnsureStartsWith

csharp/Lib/Utils/StringUtils.cs

@@ -352,6 +352,34 @@ public static class StringUtils
     }
 
 
+    public static String TrimStart(this String target, String trimString)
+    {
+        if (String.IsNullOrEmpty(trimString)) return target;
+
+        var result = target;
+        while (result.StartsWith(trimString))
+            result = result[trimString.Length..];
+
+        return result;
+    }
+
+
+    public static String TrimEnd(this String target, String trimString)
+    {
+        if (String.IsNullOrEmpty(trimString)) 
+            return target;
+
+        var result = target;
+        while (result.EndsWith(trimString))
+            result = result[..^trimString.Length];
+
+        return result;
+    }
+
+    public static String EnsureStartsWith(this String target, String prefix)
+    {
+        return $"{prefix}{target.TrimStart(prefix)}";
+    }
 
 
 }