X1 Yoga - Map stylus to touchscreen

On the X1 Yoga Gen 8, if you connect an external screen, the touch area assumes that it spans over *both*.

List the input:
```
$ xinput list
⎡ Virtual core pointer                          id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ USB HID Gaming Keyboard Consumer Control  id=19   [slave  pointer  (2)]
⎜   ↳ SYNA8017:00 06CB:CEB2 Mouse               id=9    [slave  pointer  (2)]
⎜   ↳ USB HID Gaming Keyboard Mouse             id=22   [slave  pointer  (2)]
⎜   ↳ Telink Wireless Receiver Consumer Control id=25   [slave  pointer  (2)]
⎜   ↳ Telink Wireless Receiver Mouse            id=23   [slave  pointer  (2)]
⎜   ↳ SYNA8017:00 06CB:CEB2 Touchpad            id=10   [slave  pointer  (2)]
⎜   ↳ TPPS/2 Synaptics TrackPoint               id=16   [slave  pointer  (2)]
⎜   ↳ Wacom HID 5346 Finger                     id=12   [slave  pointer  (2)]
⎜   ↳ Wacom HID 5346 Pen Pen (0x8320a638)       id=28   [slave  pointer  (2)]
⎣ Virtual core keyboard                         id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Video Bus                                 id=6    [slave  keyboard (3)]
    ↳ Power Button                              id=7    [slave  keyboard (3)]
    ↳ Sleep Button                              id=8    [slave  keyboard (3)]
    ↳ USB HID Gaming Keyboard Consumer Control  id=20   [slave  keyboard (3)]
    ↳ USB HID Gaming Keyboard                   id=21   [slave  keyboard (3)]
    ↳ Intel HID events                          id=14   [slave  keyboard (3)]
    ↳ USB HID Gaming Keyboard                   id=18   [slave  keyboard (3)]
    ↳ sof-hda-dsp Headphone                     id=13   [slave  keyboard (3)]
    ↳ Telink Wireless Receiver Consumer Control id=26   [slave  keyboard (3)]
    ↳ Telink Wireless Receiver                  id=24   [slave  keyboard (3)]
    ↳ Telink Wireless Receiver System Control   id=27   [slave  keyboard (3)]
    ↳ Wacom HID 5346 Pen                        id=11   [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=15   [slave  keyboard (3)]
    ↳ ThinkPad Extra Buttons                    id=17   [slave  keyboard (3)]
```
We are interested in the finger (id=12) and the pen (id=28).
Map those to the laptop screen:
`xinput --map-to-output 12 eDP-1`
`xinput --map-to-output 28 eDP-1`


You might need to install `xf86-input-wacom`, `libwacom` and/or, `wacomtablet` for them to be correctly detected by xinput.

It was already the case on Gen2: https://bbs.archlinux.org/viewtopic.php?id=234212

--------
If you want to change the resolution on the screen (eg. to mirror a projector), the scaling also might need to change, say from 1920*1200 to 1920*1080. The *transformation matrix* needs to change.

Settings that work well:
`xinput set-prop "Wacom HID 5346 Pen stylus" --type=float "Coordinate Transformation Matrix" 1 0 0 0 1.1 -0.05 0 0 1`