MnemonicAttached: Rework event filter
Currently, every single attached property instance would install an event filter on the window. Instead, use a singleton and install it on qGuiApp.
This is also in line with what Breeze style does. Installing it on qGuiApp also saves us the trouble with render windows. It seems the event handling is pretty wonky in complicated nested window setups like System Settings, where the render window isn't determined in time.
Opened System Settings, hit Alt, my mnemonics showed up reliably now. Before that on the landing page it wouldn’t work for some reason, only when I switched to other KCMs and back.
Breeze has had an event filter on qApp
for the longest time without checking for the window active btw.
Edited by Kai Uwe Broulik