The raw pointer button events intercepted in the XInput2 input filter
get sent through the Platform to the PointerInputRedirection. This
makes the PointerInputRedirection track the pointer button state and
emit the signals for button changed and axis changed.
These signals are used by the modifier-only shortcut detection to
determine whether the shortcut should trigger.
On X11 the "normal" input handling doesn't use the InputRedirection
and the emitted signals are not consumed by anything else. As
PointerInputRedirection is not inited the events are not forwarded
to the input filter, thus won't be processed by other parts and
won't interfere with the normal event processing on X11.
Given that it also doesn't matter that the input filter does not
apply the left-handed setting. The internal tracking will have a
wrong mouse button, but nothing is going to do decisions based on
the value of the pressed mouse button. For the moment all we are
interested in is that a button is pressed.