It's apparently not possible to set WA_TranslucentBackground after
show(). The MainWindow constructor calls applyKonsoleSettings() which
calls KMainWindow::setAutoSaveSettings() which in turn calls
setVisible(true), which makes any calls to setTransparency() from the
Application::newMainWindow() irrelevant, even if updateUseTransparency()
is called from it.

REVIEW: 128669
BUG: 366368