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Add a driver providing a tablet-mode switch input device for Microsoft
Surface devices using the Surface Aggregator KIP subsystem (to manage
detachable peripherals) or POS subsystem (to obtain device posture
information).

The KIP (full name unknown, abbreviation found through reverse
engineering) subsystem is used on the Surface Pro 8 and Surface Pro X to
manage the keyboard cover. Among other things, it provides information
on the positioning (posture) of the cover (closed, laptop-style,
detached, folded-back, ...), which can be used to implement an input
device providing the SW_TABLET_MODE event. Similarly, the POS (posture
information) subsystem provides such information on the Surface Laptop
Studio, with the difference being that the keyboard is not detachable.

As implementing the tablet-mode switch for both subsystems is largely
similar, the driver proposed in this commit, in large, acts as a generic
tablet mode switch driver framework for the...