[NavigationBar] Fixing NavBar style during willMove(toWindow:)

[DanielMorM]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

In willMove(toWindow:), we call updateColors(for:) with the wrong NavigationItem. Let's make sure we get the correct one by calling (actualStyleAndItem(for:)

Verification

Navigation bar style is applied correctly in willMove(toWindow:)

Pull request checklist

This PR has considered:

• Light and Dark appearances
• iOS supported versions (all major versions greater than or equal current target deployment version)
• VoiceOver and Keyboard Accessibility
• Internationalization and Right to Left layouts
• Different resolutions (1x, 2x, 3x)
• Size classes and window sizes (iPhone vs iPad, notched devices, multitasking, different window sizes, etc)
• iPad Pointer interaction
• SwiftUI consumption (validation or new demo scenarios needed)
• Objective-C exposure (provide it only if needed)

Microsoft Reviewers: Open in CodeFlow