Custom lock behavior can now be defined and actively used in the
keyboard.
A lock is toggled by typing a key, containing reference to the root
variable definition (`compatible = "zmk,behavior-custom-lock.yaml"`).
In order to have "A pressed -> Lock pressed -> A released" behave
correctly, this commit introduces a queue for currently pressed keys.
A release of such a key would then release the previous used behavior,
instead of the behavior the current lock state would suggest.
The size of the queue can be adjusted with `ZMK_BHV_LOCK_KEY_MAX_HELD`
Signed-off-by: Sophie Tyalie <dev@flowerpot.me>
34d9eb0e96