[StackableSnackbar]Adding dismissable property to individual snackbars

[pranjal-glowingstar]

Problem :-

Currently the ui component supports swipe to dismiss behavior and that can be configured at the stack level and not at the individual message level.
As of the design we require individual message to have different behavior for swipe to dismiss. Ask over here is to move this behavior to individual message level rather than having at the container level.

Root cause :-

The flag for enableSwipeToDismiss is at snackbar level and not at message level.

Fix :-

The functionality is now added per individual message level now. Flag is shifted from stack to SnackBarItemModel. Usecase will now have power to define which message to be dismissible and which one not.

Validations :-

Build successful and behaviour is working as expected.

(how the change was tested, including both manual and automated tests)

Screenshots

Before	After
Screenshot or description before this change	Screenshot or description with this change

Pull request checklist

This PR has considered:

• Light and Dark appearances
• Automated Tests
• Documentation and demo app examples
• VoiceOver and Keyboard Accessibility
• Internationalization and RTL layouts
• Size classes and window sizes (notched devices, multitasking, different window sizes, etc)

[pranjal-glowingstar]

@microsoft-github-policy-service agree company="Microsoft"