AutoSIP: implement new solution for handling automatic keyboard visibility

QApplication has a function QApplication::setAutoSipEnabled(bool). This is only a solution for widgets, and is also not respected on several platforms. We need to rethink if:

• it should be up to each platform to specify/decide if autoSIP should be on?
  • if yes, should we then add a new QPlatformTheme hint? And deprecate/forward the one in QApplication?
• should we add/move the autoSIP property to QGuiApplication instead? And force each plugin to follow this property?
  • note that the property should probably have the same default value on all platforms unless we want apps to have unforeseen cross platform differences/bugs
• Should we instead always use autoSIP on all platforms, and implement this using one cross-platform code base in e.g QInputMethod.
  • and perhaps add a new IM property that lets individual input controls switch this off per control?