[MVUX] Add support for grouping on ListFeed

[dr1rrb]

What would you like to be added:

Ability to group items of a ListFeed

Questions:

1. How do we support pagination?

   • If paginated source list is ordered per date, we should be able to group items per week/month
   • Do we need some specific list feed factory to build grouped collections?

2. How do we expose grouped collection to the view?

   • ICollectionView does support grouping (only one level?)

3. How to support multi-level grouping (tree view)

Why is this needed:

E.g. a list of notification grouped like:

• Today
  • Notif 1
  • Notif 2
• Yesterday
  • Notif 3
  • Notif 4
• This week
  • Notif 5
  • Notif 6
  • Notif 7

For which Platform:

• [x] iOS
• [x] Android
• [x] WebAssembly
• [x] WebAssembly renders for Xamarin.Forms
• [x] Windows
• [ ] Build tasks

[Poly-A]

Has there been any further developments with this? It would be very useful for development of an agenda/timeline control.