SurfaceInterface::inputIsInfinite() has been dropped. If the surface has
no any input region specified, SurfaceInterface::input() will return a
region that corresponds to the rect of the surface (0, 0, width, height).

While the new design is more robust, for example it's no longer possible
to forget to check SurfaceInterface::inputIsInfinite(), it has shown some
issues in the input stack of kwin.

Currently, acceptsInput() will return false if you attempt to click the
server-side decoration for a surface whose input region is not empty.

Therefore, it's possible for an application to set an input region with
a width and a height of 1. If user doesn't know about KSysGuard or the
possibility of closing apps via the task manager, they won't be able to
close such an application.

Another issue is that if an application has specified an empty input
region on purpose, user will be still able click it. With the new
behavior of SurfaceInterface::input(), this is no longer an issue and it
is handled properly by kwin.