Currently the mouse cursor jumps in unexpected ways, when a `ViewPanner`
is used in SubViewports or embedded Windows.
This is caused by providing wrong coordinate systems to
Input::warp_mouse_motion.
This PR replaces the use of `Input::warp_mouse_motion` with
`Viewport::wrap_mouse_in_rect` and makes sure, that the correct
coordinate systems are used.
This change makes it necessary, that all classes, that currently
use ViewPanner, need to provide the correct Viewport to ViewPanner.
4887172a59