[UWP] Fixed sync of ListView items with ListViewProxy

[paymicro]

Description of Change

ItemsSource wrapped in an ObservableCollection
Added processing for adding and removing items.
Screencast: https://www.screencast.com/t/LrPoEiM8a6v0

Bugs Fixed

Fixes #2485
Fixes #2809

API Changes

--

Behavioral Changes

Correct Items shown when the collection is changed

PR Checklist

• Has tests (if omitted, state reason in description)
• Rebased on top of master at time of PR
• Changes adhere to coding standard
• Consolidate commits as makes sense

[rmarinho]

@hartez can you run uwp tests on this?

[rmarinho]

this doesn't fix #2486 i wonder if the root cause si not the same.

[paymicro]

@rmarinho in #2486 more serious problem with equals string items in different groups.
In test when creates a first cell in second group

Xamarin.Forms/Xamarin.Forms.Platform.UAP/CellControl.cs

Line 355 in 4c92ed3

var indices = templatedItems.GetGroupAndIndexOfItem(context);

templatedItems.GetGroupAndIndexOfItem("I am a short text") returns the first cell of the first group.
The second group begins to have cells of the first group.

[hartez]

This currently fail the test in Issue1875.

[hartez]

When I run the Issue 1875 test with these changes, I get an ArgumentOutOfRange exception:

   at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
   at System.Collections.ObjectModel.Collection`1.Insert(Int32 index, T item)
   at Xamarin.Forms.Platform.UWP.ListViewRenderer.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
   at Xamarin.Forms.Internals.TemplatedItemsList`2.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Xamarin.Forms.Internals.TemplatedItemsList`2.OnProxyCollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
   at Xamarin.Forms.ListProxy.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at Xamarin.Forms.ListProxy.<>c__DisplayClass33_0.<OnCollectionChanged>b__0()
   at Xamarin.Forms.ListProxy.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
   at Xamarin.Forms.ListProxy.WeakNotifyProxy.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
   at System.Collections.ObjectModel.ObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at System.Collections.ObjectModel.ObservableCollection`1.InsertItem(Int32 index, T item)
   at System.Collections.ObjectModel.Collection`1.Add(T item)
   at Xamarin.Forms.Controls.Issue1875.MainViewModel.<LoadData>d__12.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at Xamarin.Forms.Controls.Issue1875.<LoadData>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at Xamarin.Forms.Controls.Issue1875.<<-ctor>b__0_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c.<ThrowAsync>b__6_0(Object state)
   at System.Threading.WinRTSynchronizationContextBase.Invoker.InvokeCore()

[jassmith]

Feel free to reopen if 1875 starts working

[paymicro]

I fixed the exception in test 1875 and append changes in the first commit.
Unfortunately, I can't reopen PR.

[StephaneDelcroix]

this PR is conflicting with #2773 that was just merged. could you please revisit ?

[paymicro]

ready!

[StephaneDelcroix]

thx