Make remote input sensitivity consistant across device DPIs

Summary:
KDEConnect's Remote Input feature does not take display DPI into account, resulting in inconsistent mouse sensitivities for devices with different DPIs.
This revision aims to fix that by dividing the mouse delta with the relative DPI of the current device. By doing so, the same amount of finger movement should produce the same amount of cursor movement, regardless of the device's DPI.

Addresses the following bug:
BUG: 391029

Reviewers: #kde_connect, nicolasfella

Reviewed By: #kde_connect, nicolasfella

Subscribers: sredman, nicolasfella, kdeconnect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D13925