Picker - Upgrade Windows to New Arch using XAML Islands

[anupriya13]

Overview

This PR upgrades the Windows implementation of the Picker component to use the new architecture based on XAML Islands. The goal is to modernize the component, improve compatibility with recent React Native Windows changes, and ensure better long-term support.

Design and Implementation

XAML Islands Integration

• The Windows Picker now leverages XAML Islands, enabling seamless integration of modern XAML controls within React Native Windows apps.
• This approach decouples the UI rendering from older Win32 components, allowing richer user interfaces and smoother theming.

Architecture Changes

• The refactored Picker internally communicates with native modules using updated bridges compatible with the latest React Native Windows architecture.
• State synchronization between JavaScript and native code has been streamlined for improved reliability and performance.
• Legacy code and obsolete workarounds tied to the previous implementation have been removed to reduce technical debt.

Spec File Changes

• All the code in “js” directory are for ios and android which remain untouched and as it is while all the code in “src” directory are for windows.
  I have removed the old implementation of windows in “js” directory for Picker.

Testing Instructions

1. Build the Windows solution in both Debug and Release modes.
2. Run the sample app and verify that Picker behaves as expected:
   • Options render correctly
   • User can select items
   • No regressions in input methods (keyboard, mouse, touch)

Note

• It has Windows changes only!
• Needs react-native 0.82+ and react-native-windows 0.82+ versions. As RNW 0.82 is not released yet, I have used canary version of RNW. Feel free to block this PR till RNW 0.82 is released for stable build.

Screenshots and videos

picker_3p_windows.mp4

[anupriya13]

@Naturalclar Please review - windows new arch picker implementation

[sundaramramaswamy]

Signing off with some comments. Please address them. LGTM otherwise!

[sundaramramaswamy]

Suggested change

	m_comboBox.HorizontalAlignment(winrt::Microsoft::UI::Xaml::HorizontalAlignment::Stretch);
	// For editable ComboBox, trigger selection change always (not just on commit)
	m_comboBox.SelectionChangedTrigger(winrt::Microsoft::UI::Xaml::Controls::ComboBoxSelectionChangedTrigger::Always);
	m_comboBox.HorizontalAlignment(
	winrt::Microsoft::UI::Xaml::HorizontalAlignment::Stretch);
	// For editable ComboBox, trigger selection change always (not just on commit)
	m_comboBox.SelectionChangedTrigger(
	winrt::Microsoft::UI::Xaml::Controls::ComboBoxSelectionChangedTrigger::Always);

Minor: fix formatting

[sundaramramaswamy]

Suggested change

	m_comboBox.Items().Append(winrt::box_value(winrt::to_hstring(item.label)));
	m_comboBox.Items()
	.Append(winrt::box_value(winrt::to_hstring(item.label)));

Minor: fix formatting.