[NET 10] Open more APIs

[pictos]

Here are a few APIs that should be open to be used by external developers (libraries and applications):

• TabbedPageManager: Making this public will allow developers to customize the TabbedPage behavior, which is nearly impossible these days.
• All MauiViews: There are some controls, like MauiSliderView that adds some behavior into a native control in order to make it work nicely with the framework. Having it internal will make it difficult to customize this control if needed. These controls should be public to allow easy customization.
• If it is not possible to make all the custom views public for .NET 10 at least make them equally in all platforms, for example, on iOS CollectionView uses MauiCollectionView which is internal, and for Android it uses MauiRecyclerView which is public.
• Expose APIs to override Managers and Delegates (macOS) easily on controls. For example, I have done this here.

Just a friendly reminder that I’m more than happy to lend a hand with this task. Let me know if there’s anything I can do to help!

[kubaflo]

I think the TabbedPageManager is the most requested to make it public, eg #27550

[kubaflo]

@pictos I've made the MauiCollectionView public here #29917

[kubaflo]

Possibly related #29540

[kubaflo]

Here another one #30750

[pictos]

Looks like we merged everything that was needed. Thanks team!