If a Wayland window is decorated the decoration size was not considered
when passing touch points to the Wayland window. For pointer input this
is considered and implemented through the input transformation matrix
which KWayland::Server::SeatInterface accepts. This should also be done
for Touch. Unfortunately the frameworks version for Plasma 5.9 is already
tagged and done and we cannot depend on new API.
Thus this change tries to workaround by calculating the proper offset
through the input transformation matrix. It isn't nice but fixes the
problem for now.
BUG: 374778