feature: blockmap debug helper cheat code

[runlow]

Expected:
Some way to optionally tell if the player-emitted tracer hitscan rays failed to collide with any monster-Thing, and if so how many, and how much of it is due to the bug. Debug overlay that helps guess in advance if the bug is going to activate.

Actual:
Although there's ways to deduce this - a lot of it is guessed and it's kind of confusing, especially since the game is fast-paced.

Possible Solutions:

• a debug cheat that you'd have to type on keyboard, such as maybe "showray" that would maybe give you some debug info to make more sense of the blockmap bug
• maybe printing the number of missed rays or something
• maybe %128 coordinates shown if that helps
• maybe showing the Thing X hitboxes
• maybe the ray could be drawn, in different colour if it misses

Why?

• sometimes not being sure if missing due to skill or due to the bug, and if it's the bug then what's a good way to avoid it, in a way that you can kinda see what's going on
• since the blockmap bug is kept in, the idea is to try to interactively understand better how it works in practice and what can be done about it
• idea is to use this hypothetical debug info and to then use the experience in normal play
• this may not be feasible or useful at all, and I get that it's kinda pedantic, just wondering if this would be good and how it could work, if at all. maybe it's not a good idea, apologies in advance

Extra:

• most of you probably know this, here's some relevant vids, if interested https://www.youtube.com/watch?v=-IYz6-KnvWU https://www.youtube.com/watch?v=MsCqLQJ1EOc
• made an issue while back on another port about this, that repo is now archived somehow show blockmap for live play (feature) coelckers/prboom-plus#228
• you can already sort of check the grid by pressing Tab for the map, then pressing g and o, guess you can already try to figure it out that way. not sure I get it still how to apply it in practice even though it's been explained, I'm sorry, I'll re-read it again