replace v6 with experimental v7 code

src/MpvNet/ExtensionMethod/PathStringExtension.cs

@@ -0,0 +1,67 @@
+
+namespace MpvNet.ExtensionMethod;
+
+public static class PathStringExtension
+{
+    public static string Ext(this string filepath) => filepath.Ext(false);
+
+    public static string Ext(this string filepath, bool includeDot)
+    {
+        if (string.IsNullOrEmpty(filepath))
+            return "";
+
+        char[] chars = filepath.ToCharArray();
+
+        for (int x = filepath.Length - 1; x >= 0; x--)
+        {
+            if (chars[x] == Path.DirectorySeparatorChar)
+                return "";
+
+            if (chars[x] == '.')
+                return filepath.Substring(x + (includeDot ? 0 : 1)).ToLowerInvariant();
+        }
+
+        return "";
+    }
+
+    public static string FileName(this string instance)
+    {
+        if (string.IsNullOrEmpty(instance))
+            return "";
+
+        int index = instance.LastIndexOf('\\');
+
+        if (index > -1)
+            return instance.Substring(index + 1);
+
+        index = instance.LastIndexOf('/');
+
+        if (index > -1)
+            return instance.Substring(index + 1);
+
+        return instance;
+    }
+
+    public static string ShortPath(this string instance, int maxLength)
+    {
+        if (string.IsNullOrEmpty(instance))
+            return "";
+
+        if (instance.Length > maxLength && instance.Substring(1, 2) == ":\\")
+            instance = instance[..3] + "...\\" + instance.FileName();
+
+        return instance;
+    }
+
+    // Ensure trailing directory separator char
+    public static string AddSep(this string instance)
+    {
+        if (string.IsNullOrEmpty(instance))
+            return "";
+
+        if (!instance.EndsWith(Path.DirectorySeparatorChar.ToString()))
+            instance = instance + Path.DirectorySeparatorChar;
+
+        return instance;
+    }
+}