Introduce `Service` for non-visual controls like Audio, Geolocator, etc.

[FeodorFitsner]

There are non-visual controls in Flet that are just wrappers around Flutter services or APIs. They need a lot of boilerplate, like subscribe/unsubscribe methods, return "empty" pixel, be added to "page.overlay" on Python side.

We could introduce a Service for non-visual services versus visual Controls.

We can have page.services collection (or dict?) or register/unregister methods for services on Python side.
On Dart side these classes could be instantiated inside root Page control and have the same life-time.
Additionally, some services could be singletons, some not.

The list of current controls that can be migrated to services:

• ...