On mixed-DPI multi-monitor setups, dialog sizes grow each time they are
reopened because logical pixel values change when a window moves between
monitors with different scaling factors. The std::max comparison during
restore guarantees monotonic growth since the DPI-scaled value always
exceeds the previously saved unscaled value.
Store width and height as DIP (device-independent pixels) using ToDIP()
on save and FromDIP() on restore. This makes the persisted size stable
regardless of which monitor the dialog was on when closed. A "dip" flag
in the JSON differentiates new DIP-format values from legacy logical
pixel values, which are converted in place on first load.
Fixes https://gitlab.com/kicad/code/kicad/-/issues/20120
Seth Hillbrand
ee8b2bebce