Use VIRTUAL_KEYBOARD_ID for injected events

The events injected via injectInputEvent will no longer be allowed to
specify an arbitrary device id.

All injected events will now come from VIRTUAL_KEYBOARD_ID.

Bug: 134977432
Test: atest libinput_tests inputflinger_tests
Change-Id: I9a61a99cf5f8ca1a27e4526dd6feedf2c1beec0f