tablet: force a distance resolution of 1

If the resolution is 0, we don't have a meaningful resolution. Use 1 instead
so we can use the resolution in future calculations instead of having to worry
about NaN.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Stephen Chandler Paul <thatslyude@gmail.com>
tablet: convert the distance axis to mm

As we say in the documentation, provide the actual distance in mm

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Stephen Chandler Paul <thatslyude@gmail.com>
tablet: provide x/y by default in mm off the top/left corner

Given that tablets may not have the same x/y resolution, raw values are mostly
meaningless and likely to be handled the wrong way. Providing x/y in mm is the
only constant, meaningful value.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Stephen Chandler Paul <thatslyude@gmail.com>
tablet: add a function to get the size of a tablet device

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Stephen Chandler Paul <thatslyude@gmail.com>