double MouseMotion events when cursor grab mode is Confined, while using X11

seems to be caused by set_cursor_mode in platform_impl/linux/x11/window.rs calling XGrabPointer with ffi::True as the 3rd (owner_events) argument.

to re-produce:
try the cursor_grab.rs example with CursorGrabMode::None, and then with CursorGrabMode::Confined.

echo focus the cursor_grab.rs example window now
gcc -o send_event send_event.c -lX11 -lXtst
sleep 1
./send_event

#include <X11/Xlib.h>
#include <X11/extensions/XTest.h>

int main(void) {
	Display *display = XOpenDisplay(NULL);
	XTestFakeRelativeMotionEvent(display, 255, 255, 0);
	XFlush(display);
	XCloseDisplay(display);
	return 0;
}

this is inconsistent with the wayland impl (and it leads to inconsistencies in camera sensitivity for example)

Start in platform_impl/linux/x11/window.rs at set_cursor_mode and reproduce the behavior with the cursor_grab.rs example using CursorGrabMode::None and CursorGrabMode::Confined. Compare the X11 pointer-grab behavior with the Wayland implementation, then verify that confined mode no longer produces duplicate mouse-motion events or inconsistent camera sensitivity.