Burst firing considers all creatures in range.

Fixes #9849

Introducing `player::get_visible_creatures` to get all visible creatures in range (includes monsters, npcs and the player character, but excludes the player object that this has been called on).

Can also be used for the other issue "list npcs along with monsters".

Edit: it should probably be mentioned that this does *not* consider friend / foe status of the creatures. This is the preexisting behavior. Is that a bug?