This way, we can use EDID comparisons also for KWin-poweredbrightness devices.
Extracted from !466 to reduce its scope. Implementing this doesn't cause any user-visible changes by default (ScreenBrightnessController::tryMatchKScreenOutput(), the only place that currently uses edidData(), already had a special case for KWin integration) but is necessary for !466 to work under KWin/Wayland. As such, this should get cherry-picked into Plasma/6.2 if !466 also makes it there.