This change implements the required changes for wl_seat version 5.
There seem to be applications which require version 5 and refuse to
start if the server doesn't provide it. Thus we need to provide it.
The main difference with version 5 is that pointer need to send a
frame event after each logical group of events. As we don't support the
new events from version 5 yet, we just emit the frame after each event
and implement the suggested semantics for the enter/leave behavior.
To really make use of this, we will have to implement additions in the
API and then in KWin to expose the new API elements. But to just support
the semantics we don't need it.