vis: keep track of most recently processed keys of input queue

Currently the key handling functions do not know through which mapping
they were invoked. As an example the `count` handler exploits the
implementation detail that the input queue is stored in contiguous
memory, meaning `keys[-1]` gives access to the digit being pressed.

This adds infrastructure to keep track of the two most recently processed
keys of the input queue.

The information is guaranteed to be accurate for the initial invocation
of the key handler but will be overwritten in case new keys are pushed
to the input queue (e.g. through vis_keys_feed).

0 files changed, 0 insertions, 0 deletions