Fix icons, darkmode and stuff.

My suggestion is

• Remove all our changes, all usage of win32 api for this and such in libkleo, kleopatra, our kiconthemes patches and so on.
• Ensure the 'common cases' works for all our software with KColorScheme, KIconThemes and whatever is in Qt6 for this
• Test the more fringe cases of weird high contrast themes
  • Fix Q* and K* for the fringe cases where it is broken and we think they should be supported