libinput-util.h is getting a bit of a catchall bucket and it includes things
like libinput-private.h which in turn includes libwacom. This makes
libinput-util.h less useful for bits that only need e.g. the string processing
utilities.
So let's split them all up in to separate files, to be used as-needed.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
