QCursor::setPos X coordinates is wrong when DPI scaling is used

QML applications (couldn't test on QWidget) on High-DPI multi-monitor setups cannot use `QCursor::setPos` reliably.

How to reproduce:

1. Use a setup with at least 2 monitors with DPI scaling enabled (200% on each screen is what I used).
2. Start the application. It will open on your primary monitor
3. Move the application's window to the other (secondary) monitor
4. Call `QCursor::setPos(x, y)`. The X coordinate will always reset to 0.

Here is a very short code snippet of the issue:

const auto offset = ...; // Some code that computes an offset
const auto currentPos = cursor->pos();
const auto newPos = currentPos + offset;
cursor->setPos(newPos);

When I run the code snippet from a window on my primary monitor I get the following log:

• `currentPos = QPoint(4419, 111)`
• `newPos = QPoint(5750, 111)`
• After calling setPos, `cursor->pos() = QPoint(5750, 111)` (equal to what was expected)

If I run this exact same code but I move my application's window to my secondary monitor, I get the following log:

• `currentPos = QPoint(582, 70)`
• `newPos = QPoint(1913, 70)`
• After calling setPos, `cursor->pos() = QPoint(0, 70)` (X coord has been reset to 0)

Configs on which I could repeat the issue:

Arch Linux

DE: Gnome 41

X server: Xorg

Qt version: 5.15.2

Primary display: 4K @200% scaling

Secondary display: 4K @200% scaling

Ubuntu 21.04

DE: Gnome 3.38.5

X Server: Xorg

Qt version: 5.15.2

Primary display: 1440p @200% scaling

Secondary display: 1440p @200% scaling

Windows 10

Qt version: 5.15.2

Primary display: 1920×1080 @150% scaling

Secondary display: 4K @200% scaling

I have a small project available that shows the example but Jira tells me there is a "missing token" when I try to upload it, I don't know how I can attach it to this message.

In the meantime the files content can be found in the last message of this ticket on Qt's forum: https://forum.qt.io/topic/132330/qcursor-setpos-sets-wrong-x-coordinates/7