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.
Without handling transform, the surface was created with the wrong size on rotated displays, causing flicker before the .configure event arrived. With, it will attempt to set the right size from the start.
