XP Pen ACK05 reports BTN_TOOL_PENCIL instead of BTN_STYLUS
libinput record
from the recording in #59 (comment 2805791) says:
# Event code 323 (BTN_TOOL_PENCIL)
but the code says
// Byte 4 in report - just exists so we get to be a tablet pad
Usage_Dig_BarrelSwitch // BTN_STYLUS