## Summary of the Pull Request
BODGY!
This solution was suggested in https://github.com/microsoft/microsoft-ui-xaml/issues/4554#issuecomment-887815332.
When the window moves, or when a ScrollViewer scrolls, dismiss any popups that are visible. This happens automagically when an app is a real XAML app, but it doesn't work for XAML Islands.
## References
* upstream at https://github.com/microsoft/microsoft-ui-xaml/issues/4554
## PR Checklist
* [x] Closes#9320
* [x] I work here
* [ ] Tests added/passed
* [ ] Requires documentation to be updated
## Detailed Description of the Pull Request / Additional comments
Unfortunately, we've got a bunch of scroll viewers in our SUI. So I did something bodgyx2 to make our life a little easier.
`DismissAllPopups` can be used to dismiss all popups for a particular UI element. However, we've got a bunch of pages with scroll viewers that may or may not have popups in them. Rather than define the same exact body for all their `ViewChanging` events, the `HasScrollViewer` struct will just do it for you!
Inside the `HasScrollViewer` stuct, we can't get at the `XamlRoot()` that our subclass implements. I mean, _we_ can, but when XAML does it's codegen, _XAML_ won't be able to figure it out.
Fortunately for us, we don't need to! The sender is a UIElement, so we can just get _their_ `XamlRoot()`.
So, you can fix this for any SUI page with just a simple
```diff
- <ScrollViewer>
+ <ScrollViewer ViewChanging="ViewChanging">
```
```diff
- struct AddProfile : AddProfileT<AddProfile>
+ struct AddProfile : public HasScrollViewer<AddProfile>, AddProfileT<AddProfile>
```
## Validation Steps Performed
* the window doesn't close when you move it
* the popups _do_ close when you move the window
* the popups close when you scroll any SUI page
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