Fix Windows Media Element in MultiWindow Mode on exit Crash

[ne0rrmatrix]

• Bug fix

Description of Change

Track window count and manage snackbar notifications

Added a static NumberOfWindows property to the Options class to track the number of windows. Updated SetShouldEnableSnackbarOnWindows to increment/decrement NumberOfWindows on window creation/closure. Conditional registration/unregistration of AppNotificationManager for snackbar notifications based on NumberOfWindows count.

Linked Issues

• Fixes [BUG] Media Element Multi-Window Page crash on app exit #2257
• Fixes Application crashes upon closing a second window when using Builder.options.SetShouldEnableSnackbarOnWindows(true)  #2279

PR Checklist

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

Additional information

This PR uses a simple counter to track the number of windows that exist and only when one is remaining will it unregister Snackview

[McSaverInvestments]

This changed fixed #2279
Hoping it will be released soon

[McSaverInvestments]

Can some please resolve this merge conflict?
We have waiting on this for quite sometime!
@brminnick @ne0rrmatrix @pictos @softlion

Copilot reviewed 1 out of 1 changed files in this pull request and generated no suggestions.

[McSaverInvestments]

I am new to this process, and don't understand who needs to do what to get this done, but I would appreciate any help to get the mission accomplished.

@brminnick @ne0rrmatrix @pictos @softlion