GUI scale settings

There was an issue #4919 about Giant UI, but maybe it's a feature to have such big buttons+fonts, because with higher resolution it becomes smaller and smaller.
So the first workaround is in settings to change it with Qt scale factor as an option inside program.
№2 make a wide screen GUI with high-res and bigger buttons and maybe some +window/widgets changes.
This is about theming i guess,№3 to provide some GUI values than can be changed without faults and big problems.

No files, tests, or entry points are named. Start by reading issue #4919 and locating the existing settings and GUI scaling implementation; first clarify whether the goal is a Qt scale-factor option, wider high-resolution layouts, configurable GUI values, or all three. Done should mean an agreed scope with defined scaling behavior and no layout faults.

Written by the indexing model from the issue text.