Move State out of AcitivityIndicator

[FichteFoll]

It was polluting the documentation.

[deathaxe]

More a Sphinx shortcomming, than a technical limitation/violation of the implementation. _State feels somewhat too generic when used as a global. And it is not more or less private that ViewTarget classes, thus probably not worth messing with underscores, as only ActivityIndicator is marked exported anyway.

[FichteFoll]

It is sufficiently namespaced by the module imo (there is no other "state" to be had for an activity indicator). Even inside the other class, it should have been written with an underscore because it is not part of the public API, in which case it most likely also would not be picked up by sphinx's autodoc, so I would argue this is a feature working as intended and not a shortcoming.

However, I still feel that using State.STOPPED is more ergonomic than self._State.STOPPED.