[AD] Suggestion: al_clear_keyboard_state()

[Beoran <beoran@xxxxxxxxxx>]

Following a discussion on the forum here:
https://www.allegro.cc/forums/thread/615411/1013663#target

I propose we implement an API function al_clear_keyboard_state() that 
clears ALLEGR's keyboatd state and sets all keys to unpressed. This 
function is mainly for use when the ALLEGRO_EVENT_DISPLAY_SWITCH_OUT 
is received, to prevent any pressed keys from getting "stuck" in the 
down state because Allegro hasn't received the key up event while the 
display wasn't active.

Would such a function be acceptable? Implementation is trivial, just a 
memset() really; but the function is a bit of a workaround, os I 
wonder if exposing such an API would be OK.

Kind Regards,

B.