With the policy being disentangled from application, it becomes testable.
This prepares for moving the entire visibility mechanism to the new class and taking away more pieces of ServerContextService.
In addition, this is a good warmup before trying to implement sizing policy.
If the corresponding a11y settings is disbaled don't unfold
the keyboad at all.
This helps e.g. running the same session on laptops or when
an external keyboard is attached.
Closes: #222
The manager is used for sizing the layer surface. It promises never to exceed half the output height.
The selection of the current layout is not being done here, leading to worse behaviour in 1:1 scaling.
In the future, it could be used for sizing the keyboard itself and the suggestion box, as well as decide which layout to use, because layouts should have some sizing hints.
Layout management was pointlessly bound with the EekboardContextService with inheritance. Splitting it out will make it easier to further break apart layout state management, settings, and input method in the future.
