InputReader: Notify policy of device changes after flushing events

...so that the rest of the listeners are synchonized with the device
changes (through NotifyInputDevicesChangedArgs) before the policy
can react to the changes.

Bug: 324061913
Bug: 293587049
Test: atest inputflinger_tests
Test: atest VirtualDeviceMirrorDisplayTest#virtualMouse_buttonEvent --rerun-until-failure
Change-Id: I818b1e688565d30867295019c5baae29cb5bdbf2