cmake-gui: Add flag to enable High DPI scaling
This Qt flag enables UI scaling based on scale factor provided by the operating system. Only supported on versions of Qt >= 5.6.
The flag has no effect on macOS, where high DPI support is already enabled as a setting in the bundle's info.plist.
Fixes: #17026 (closed)
Topic-rename: cmake-gui-high-dpi
Edited by Brad King