KeyboardInterface is a multiplexer, it has a global state to kwin
that forwards events the single focussed window.
XWayland also forwards events to clients, but uses the keyboard interface.
It has some overloads that take a specific client, this was used for key events
but not modifiers.
The end result was not only that XWayland could miss a modifier update, but
also that wayland clients would get modifier updates out of order.
Key events must come first.
BUG: 490270
374d859493