Client: Fix the mouse being stuck in pressed state after DnD

I can still reproduce the problem using QtWidgets applications on KDE Plasma 5.27. Both Windows and macOS QPA have a similar quirk and they both send a MouseButtonRelease event rather than a MouseMove event.

Amends f7a386ee

Task-number: QTBUG-97037 Pick-to: 6.5 6.2 5.15 Change-Id: I864a1cb68b3660d858623f943b3958f7cafbf955 Reviewed-by: David Edmundson davidedmundson@kde.org (cherry picked from commit e3c74961)