Writing on adjacent squares, not just the floor

[ashGlaw]

Is your feature request related to a problem? Please describe.

Using permanent markers or spray cans or what have you to write on the floor is very useful. I see graffiti on the walls of some evac shelters. But there doesn't seem to be a means of using a writing implement on an adjacent square. That's a shame, because writing on walls is shown to be possible through the evidence of graffiti.

Describe the solution you'd like

When you activate a writing implement the menu that pops up should have a third option letting you write a message on an adjacent surface. It probably shouldn't work on spaces you can walk through, only spaces that block your path. It probably shouldn't be restricted to walls, you can write on most things

Describe alternatives you've considered

We could make walls act like signs and ask if you want to change the message, but I think making every wall activateable would be exceptionally tedious and would discourage a player from even carrying a writing implement.

Additional context

If this could be accomplished through json then I could take a stab at it, but I don't know the first thing about tackling C++