libwacom needs to differentiate between Wacom and non-Wacom styli

[whot]

See #636 where we have the first case of a tool apparently sending a tool id (0x1) but it's a 0x27C6 Goodix device rather than a Wacom device. Our stylus description for 0x1 doesn't match the device in question.

This is going to be rather interesting because our APIs implicitly assume a Wacom vendor ID.

cc @Neolanco