Added WorldHitscanFired and WorldHitscanPreFired

[jekyllgrim]

This adds WorldHitscanFired and WorldHitscanPreFired events to P_LineAttack and P_RailAttack. The former is called after a hitscan has been fired and provides information about it; the latter before it and allows stopping it. The idea is to allow mod authors universally detect hitscans, and potentially replace them with projectiles, which hasn't been possible so far.

THE PROBLEM is that in its current form, despite compiling properly, it leads to a mysterious crash on startup, presumably tripping up the file system. This is caused by WorldHitscanPrefired specifically; the other features were tested and work fine, but as soon as I added WorldHitscanPrefired, the crashes started happening. Unfortunately, I cannot nail down the issue myself.

UPD: I can't believe my inattention; the whole problem was that WorldHitscanPreFired was defined without a return value in zscript, and apparently that causes a CTD on startup rather than a build error.

Test file. This replaces hitscans with plasma balls and reports on received values.
WorldHitscan.zip

[madame-rachelle]

Yeah it's hard to pin down the issue with this code since it trips up something else entirely within the new file system.

[MajorCooke]

Report it as a bug. If anything, Graf can take a look at it.

[jekyllgrim]

Report it as a bug. If anything, Graf can take a look at it.

That's what I'm doing, more or less? I can't really report it as a bug for the current version of GZDoom because this issue occurs only after my personal changes on the cpp side.

[jekyllgrim]

This is finally fixed and tested. No performance impact that I could see.

[jekyllgrim]

Replaced DVector3 with const DVector3& following Boondorl's suggestion.