GUI doesn't rescale properly using RDP with different display scaling on Windows with Qt5

[srcejon]

On Windows with Qt5, the GUI doesn't rescale properly when connecting via Remote Desktop Protocol (RDP) and the client's display scaling setting differs from the server. For example:

• Run SDRangel on Windows with scaling set to 100%
• Remote Desktop to that PC with client scaling set to 200%
• Font will be too large, some other UI elements too small

Fiddled with it for a few hours, but can't see how to fix it.

It does seem to work OK with Qt 6.6.1, so possibly the first reason to switch to Qt 6 on Windows. Need to review what doesn't currently work in Qt 6 (The Mac arm build uses 6).