Schedule notification Id is empty while getting notification from GetScheduledToastNotifications method

**Describe the bug**
I have set `Id` for Schedule notification when creating toast notification. But, Schedule notification Id is empty while getting notification from `GetScheduledToastNotifications` method and `ScheduledToastNotificationShowing` event in Winui_desktop project.

**Steps to reproduce the bug**
1. Run the attached sample and click reminder button in current application.
2. Snooze reminder with 15 minutes.
3. Put a break point on `Notification_Click` method.
4. Then, once again click reminder button in current application.
5. Check Item Id value in foreach loop. Notification Id will be empty.

**Expected behavior**
Need to maintain same notification Id to check and ignore snoozed reminders(notifications).

**Screenshots**

**Version Info**

NuGet package version:

[WinUI 3 - Project Reunion 0.8 Preview: 0.8.0-preview]
[WinUIToastNotifier_Desktop.zip](https://github.com/microsoft/microsoft-ui-xaml/files/6831141/WinUIToastNotifier_Desktop.zip)

Windows app type:
| UWP | Win32 |
| :--------------- | :--------------- |
| Yes| Yes|

| Windows 10 version | Saw the problem? |
| :--------------------------------- | :-------------------- |
| Insider Build (xxxxx) | |
| October 2020 Update (19042) | |
| May 2020 Update (19041) | Yes |
| November 2019 Update (18363) | |
| May 2019 Update (18362) | |
| October 2018 Update (17763) | |
| April 2018 Update (17134) | |
| Fall Creators Update (16299) | |
| Creators Update (15063) | |

| Device form factor | Saw the problem? |
| :----------------- | :--------------- |
| Desktop | Yes|
| Xbox | |
| Surface Hub | |
| IoT | |

**Additional context**