Backend Preferences

[MiaKoring]

With expanding featureset, platformsupport and optimization there may be more and more differences which patterns work best on which backend, one example would be prefering in-place swap over add-remove, like described in #300

If we notice this happening more, we might want to separate those traits out, so they are not just inside the main AppBackend class.

Instead there could be an SCUI-Level structure BackendTrait where the information can be accessed centralized and used for pattern-optimized implementations on SCUI level.

AppBackend would get a new protocol requirement:

var traits: BackendTraits { get }