Use XamlBindingHelper setters in tests

Replace manual boxing and SetValue calls with global::Windows.UI.Xaml.Markup.XamlBindingHelper.SetPropertyFrom* calls across the dependency property generator tests. Update DataRow entries to include the target set method name and refactor the test helper to compute the setter body based on an optional setMethodName parameter. Add a new test (SingleProperty_Int32_WithNoCaching_WithObjectSetCallback) covering an int property with an object-based OnNumberSet callback to validate generated code that mixes object set callbacks and optimized XamlBindingHelper setters.

Co-Authored-By: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Sergio0694