[Spec] Implement ContentView inside Core

[jsuarezruiz]

[The feature]

The ContentView class is a type of Layout that contains a single child element and is typically used to create custom, reusable controls.

The ContentView class defines a single property, Content is a View object.

To allow porting libraries and apps to .NET MAUI it is important to have ContentView implementation in Core.

Difficulty : [low]

[PaulAndersonS]

When will this support will be released?

[mattleibow]

Just thinking we might actually have this already... In bits. I added a IContentView for the page changes, and this is essentials the same. And, the PageHandler actually takes IContentView since we no longer have IPage.

It might just need a mapping from ContentView to PageHandler