Add lifecycle docs for views

[mattleibow]

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

[mattleibow]

@PureWeen am I missing some? Is there any order or platform differences?

[MartyIX]

This would be really helpful to document.

Especially, it would be great to know how to emulate "dispose" behavior for custom controls - i.e. should one use the combination of Loaded & Unloaded or implement IDisposable on custom controls?

Possibly related questions:

• https://github.com/dotnet/maui/discussions/14908
• https://github.com/dotnet/maui/discussions/18246