This context is meant to hold the state and the backend.
Currently it is not possible to have several platform at the same time in one process, but in the future it might be.
See issue #4294
Internal function to set a hook that’s invoked whenever a slint::Window is shown. This
is used by the system testing module. Returns a previously set hook, if any.
Internal function to access the context.
The factory function is called if the platform abstraction is not yet
initialized, and should be given by the platform_selector