[iOS, Android] Fix when we call ReloadData on CollectionView, Fix issue adding item to start of Collection on ANdroid

[rmarinho]

Description of Change

I found that #9911 introduced a new concept of Reload the CollectionView if it wasn't visible and an update to the items was in progress.
Seems this approach doesn't work well when we push a modal on top of the CollectionView and then on dispose we add/remove items from the CollectionView. This was actually preventing the item from being removed. So my first try was to remove the check for _collectionViewController.View.Window == null , this worked but was going around the real problem.

It seems that also the _batchUpdating.WaitAsync() on the Reload method isn't working as expected, it was getting stuck because there were no available threads on the _batchUpdating semaphore. The problem was after a BatchUpdates was executed (for example add a item) the semaphore wasn't releasing and making the threads available. So the next time for example if it wanted to Reload it was getting stuck.

Fix issue on Android that Scrolling to the current position when adding an item would scroll the last item.

This is actual a regression from previous versions.

Issues Resolved

• fixes [Bug] [iOS] ObservableCollection.RemoveAt(index) with a valid index raises ArgementOutOfRangeException. #10300

API Changes

None

Platforms Affected

• iOS

Behavioral/Visual Changes

None

Before/After Screenshots

Not applicable

Testing Procedure

Added UITest 10300
Click Add
Click Delete
Click Close,
You should see the item 2

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[rmarinho]

Not sure if we should still would remove this check https://github.com/xamarin/Xamarin.Forms/blob/4.6.0/Xamarin.Forms.Platform.iOS/CollectionView/ObservableItemsSource.cs#L287

_collectionViewController.View.Window == null

In the issue i created Window is null because we were showing a Modal and going back to the page with collectionview

[samhouts]

Test failed on Android API 19