Adapt the sanitized pointer handling, discussed at #17196:
Wayland driver specific changes:
- make sure pointer position is always within [-0x7fff,0x7fff]
by using the confined wrapper
- enable lightgun to report -0x8000 if pointer is really offscreen
- remove extra "inside" checks
- report same pointer/lightgun coordinates for all ports
- simplify pointer and lightgun handling
Other changes:
- unify "offscreen" condition through input_driver.c
- slight tuning of pointer conversion in video_driver.c
- update libretro.h with explanation and pointer offscreen value
- small fixes on remote retropad test screen
072d949346