Add lifecycle docs for views

We have docs on app/window lifecycle, but not for individual views. Some events that I see are:

Before properties set:

- **Constructor**

After properties set:

- **HandlerChanging event** - before the view is assigned a handler (but also if a new handler comes in)
- **HandlerChanged event** - after the view is assigned a handler (but also if there is a new handler)
- **Loaded event** - the view is attached to the UI (and again if it is detached and re-attached)
- **Unloaded event** - the view is detached from the UI (and again if it is re-attached and then detached again)

See also https://github.com/dotnet/maui/issues/4071