Fix implementation of getDX/getDY/getDWheel to reset the value to 0 after a call, like LWJGL2 docs specify (the original lwjglx implementation was broken)
Suppress mouse movement events on mouse grabs/ungrabs and send a fake event to make sure the correct GUI slot is highlighted when GUIs are opened, and the camera doesn't move when GUIs are closed. This is now much more reliable than the previous incomplete workaround.