Fix windows multi window crash on Full Screen

[ne0rrmatrix]

• Bug fix

Description of Change

Improve layout and fullscreen handling for MediaElement

• Wrap content in ScrollView in MediaElementCarouselViewPage.xaml
• Replace Border with Grid in MediaElementCollectionViewPage.xaml
• Use Grid for complex layout in MediaElementMultipleWindowsPage.cs
• Add method for foreground window handle in MauiMediaElement.windows.cs
• Refactor AppWindow retrieval and fullscreen handling logic
• Add methods for screen size retrieval and popup configuration

Linked Issues

• Fixes #2255

PR Checklist

• [x] Has a linked Issue, and the Issue has been approved(bug) or Championed (feature/proposal)
• [ ] Has tests (if omitted, state reason in description)
• [x] Has samples (if omitted, state reason in description)
• [x] Rebased on top of main at time of PR
• [x] Changes adhere to coding standard
• [ ] Documentation created or updated: https://github.com/MicrosoftDocs/CommunityToolkit/pulls

Additional information

This does not fix all issues with multi window environments in Windows. There is another issue where snackbar option is enabled crashes the app. I will be creating a bug report for that seperately.