Summary:
KWin passes the current keysym converted to a Qt::Key in the QKeyEvent.
The current keysym does not always change when a key gets released, so
when pressing a shortcut the release carry a Qt::Key which could be
considered as wrong.

QtWayland transforms the actual pressed/released key into a keysym and
passes that through the QKeyEvent. This change does the same for the
internal windows. A new QKeyEvent is created and adjusted in a way that
it matches what Qt expects.

Why not change everything to how Qt expects it? The key is used at
various places and in KWin internally we expect the behavior how it is
currently implemented. So it's better to use Qt's expectation only when
interacting with Qt.

Also the change carries a workaround for a bug in QKeySequenceEdit
(see QTBUG-62102) and transforms Super to Meta. As this adjustment only
makes sense for the internal windows we need to send in an adjusted
QKeyEvent anyway, so another arg...