[Request] Allow self-registration of handlers, etc.

Description

Imagine a library with a big amount of handlers, effects, etc.

• If a client-dev wants to use the components - he needs to put a lot of code in the CreateMauiApp() method. If the client-dev uses a NuGet - it will not be obvious that there is an additional step he needs to do to get the components working.
• We can implement a single UseLibrary() extension method, but there are huge consequences for using such an approach. The problem is as follows - in the UseLibrary() method, we need to register everything - all handlers, renderers, effects, everything. Now the linker will not be able to strip away unused code - even if the client-dev uses only a couple of our controls.
• It will be very useful if we can introduce a property in the MauiApp class that will allow to dynamically register a handler. For example, the static constructor of a Component1 can execute a call like MauiApp.Current.TryAddHandler(Component1, Component1Handler). This way if a client-dev uses Component1 - the handler will be registered automatically. If the client-dev does not use it - the linker would be able to properly strip away the component and the handler. Note that the name of the method is TryAddHandler() - so it can check if a handler was already registered for this type and not overwrite it.

Public API Changes

We have to analyze possibilities to allow this.

Intended Use-Case

MauiApp.Current.TryAddHandler(Component1, Component1Handler)

[dotMorten]

I support this 1000%. I’m already time after time again seeing people not understanding why our controls don’t work, simply because they didn’t know they needed to call some obscure UseXxx() method in the builder. While I get the technical reason for it, it is incredibly developer unfriendly for 3rd party component customers.

[msftbot[bot]]

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