Fix-7167-UWP-ListViewRenderer-ScrollToTop-when-NotifyCollectionChangedAction.Reset...

Fix-7167-UWP-ListViewRenderer-ScrollToTop-when-NotifyCollectionChangedAction.Reset (#7279)

* - created test view in control gallery for issue 7167
- wrote view, vm, and "ImprovedObservableCollection" for testing purpose
- reproduced the bug without using any external nugets like "System.Reactive"
- added onitemselected of listview to test itemselections
- fixed by changing the implementation of Xamarin.Forms.Platform.UWP.ListViewRenderer.ReloadData
- single commit which is useful for cherry picks
- if itemsource and collectionviewsource.source (_collection) are the same the collectionviewsource is not being reinstantioated again
- wrote ui test.

* - changed controlgalery.projitems manually after cherrypick

* - made testcase uitestable

* - fixed uitesting exception

* - made view, vm ui-testable
- (TODO) modified uitest. (assert is missing)

* - created test view in control gallery for issue 7167
- wrote view, vm, and "ImprovedObservableCollection" for testing purpose
- reproduced the bug without using any external nugets like "System.Reactive"
- added onitemselected of listview to test itemselections
- fixed by changing the implementation of Xamarin.Forms.Platform.UWP.ListViewRenderer.ReloadData
- single commit which is useful for cherry picks
- if itemsource and collectionviewsource.source (_collection) are the same the collectionviewsource is not being reinstantioated again
- wrote ui test.

* - changed controlgalery.projitems manually after cherrypick

* - made testcase uitestable

* - fixed uitesting exception

* - made view, vm ui-testable
- (TODO) modified uitest. (assert is missing)

* - wrote uitest, formetted

* - updated comments

* - uitest are only being executed for UWP

* - removed comments (PR feedback)