[Bug] iOS CellView BindingContextChanged Event -> Null Reference Within ContextActions Clear()

[breezy64]

Description

On iOS, a null reference exception get's thrown if ContextAction.Clear() is called within the BindingContextChanged callback
of a ViewCell within a ListView. The problem seems to only happen when scrolling a very large list and the RecycleElement Caching strategy is is used

This is probably related to #10934

Steps to Reproduce

1. Create a ListView.
2. Assign the ListView's ItemTemplate to a ViewCell
3. Add some ContextActions to the ViewCell
4. Add a callback for the View Cell's BindingContextChanged event
   i) Call ContextActions.Clear() within the callback
5. Populate a list view with items (the more the better)
6. Keep scrolling until it crashes

Expected Behavior

Don't crash when scrolling a listview (given that the list view's individual cells might have changing context actions)

Actual Behavior

App crashes with a null reference exception

Basic Information

• Version with issue: 4.8.0
• Last known good version: N/A
• IDE: Microsoft Visual Studio Enterprise 2019 Version 16.7.2
• Platform Target Frameworks:
  • iOS: Deployment Target 13.6
• Nuget Packages:
  • Rg.Plugins.Popup, Version=2.0.0.2
  • Xamarin.Forms, Version=4.8.0.1269
  • Xamarin.Essentials, Version=1.5.3.2
  • Newtonsoft.Json, Version=12.0.2

Stack Trace

`
SIGABRT: Object reference not set to an instance of an object

ContextActionsCell.OnContextItemsChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) D:\a\1\s\Xamarin.Forms.Platform.iOS\ContextActionCell.cs:488
(wrapper delegate-invoke) .invoke_void_object_NotifyCollectionChangedEventArgs(object,System.Collections.Specialized.NotifyCollectionChangedEventArgs)
ObservableCollection1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e) ObservableCollection1[T].OnCollectionReset ()
ObservableCollection1[T].ClearItems () Collection1[T].Clear ()
TimesheetListItemViewCell.OnBindingContextChanged ()
`