Add concrete ConvertEventHandler example to AddHandler statement documentation

[Copilot]

The AddHandler statement documentation previously contained only a basic example with simple custom events. This PR enhances the documentation with a practical, real-world example demonstrating AddHandler usage with ConvertEventHandler delegates for data binding scenarios.

Changes Made

Enhanced Example Code (VbVbalrEvents/VB/Class1.vb snippet17):

• Added a comprehensive DataBindingExample class showing Windows Forms data binding
• Demonstrates using AddHandler to attach ConvertEventHandler delegates to Format and Parse events of a Binding object
• Shows practical decimal-to-currency conversion scenarios commonly used in business applications
• Maintains the original simple example for basic AddHandler usage patterns

Updated Documentation (addhandler-statement.md):

• Added detailed explanation of the ConvertEventHandler scenario
• Provided clear context about data binding use cases
• Listed key concepts demonstrated in the example
• Follows Visual Basic documentation style guidelines

Example Overview

The new example shows how to:

' Create a binding and use AddHandler with ConvertEventHandler
Dim binding As New Binding("Text", ds, "Orders.OrderAmount")
AddHandler binding.Format, AddressOf DecimalToCurrency
AddHandler binding.Parse, AddressOf CurrencyToDecimal

This provides developers with a concrete, practical demonstration of AddHandler usage beyond simple event scenarios, addressing the need for more explicit examples similar to those found in the Microsoft ConvertEventHandler documentation.

Fixes #21347.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.