Bug 2403284

This has been tested on a ThinkBook 14 2-in-1 and a ThinkPad X13 Yoga Gen 3. 
Both laptops have a touchscreen (with pen input) and run at 1920x1200.
At the native resolution the touchscreen is mapped to the screen perfectly, so the touch appears below the fingertip.

Changing the resolution to 1920x1080 (16:9), as is sometimes needed to mirror with external screens/projectors, breaks the mapping of the touchscreen.

On the centre line (half way up), the mapping stays perfect. Above the centre line the touch is lower than the the fingertip and below the centre line the touch is above the fingertip. The distance between fingertip and touch increases as you move away from the centre line.

The mapping of the touchscreen either stays on 1920x1200 or it is wrong when at 1920x1080.

In general, any 16:10 resolution (eg 1680x1050) works fine, and any 16:9 resolution (eg 1600x900) has the issue.

This is obviously an issue as once an external screen is connected that cannot do 1920x1200 and needs a 16:9 resolution to maintain its geometry, the touch control of the laptop(s) is finicky at best. 

The pen input is also affected, and it's impossible to use the pen to write.

Reproducible: Always

Steps to Reproduce:
1. Set resolution to any 16:9 from 16:10 (from 1920:1200 to 1920:1080)
2. Try to move windows by grabbing the header bar.  The higher above the centre line the header bar is, the further up your fingertip must be from it to grab it. 
Actual Results:
The fingertip and the touch point on the desktop are off. The pen tip and the line drawn are off. They are perfectly aligned on the centre line of the screen, but once you are above the centre line (closer to the top of the screen) the line appears below the pen tip (and touch below the finger tip), and if you go below the centre line (close to the bottom of the screen), the line appears above the pen tip (and the touch also above the finger tip).

Expected Results:
The line appears at the tip of the pen everywhere on the screen. 

Additional Information:
I've played with some udev rules and I can change the mapping when at 1080p but I cannot find how to fix the offset as it is not constant.