iw3 replaceFunc

[regenerance]

PR: Add GSC replaceFunc support for IW3 multiplayer

Summary

This change adds a new GSC builtin, replaceFunc, that allows one GSC function
to be replaced by another function at runtime. It is intended for mods that
need to override or extend existing script behavior without editing the
original function directly.

What replaceFunc does

replaceFunc takes two function references:

replaceFunc(originalFunction, replacementFunction);

The first function is the function to intercept, and the second function is
the function that should run in its place. The replacement is registered by
the compiled code positions of both functions. When the script VM is about to
execute a registered original function, the VM hook resolves that code
position to the replacement code position and continues execution from the
replacement function.

This makes it possible for a mod to redirect existing script callbacks or
functions while leaving the original game script files unchanged.

Implementation details

• Registers replaceFunc as a GSC builtin available to all builtin contexts.
• Validates that exactly two parameters are supplied.
• Validates that both parameters are actual function values.
• Tracks replacements by compiled GSC code position.
• Hooks VM execution so replacements are applied whenever the original
  function is called.
• Includes registration, replacement-hit, and cleanup logging to make the
  behavior easy to verify during development.
• Installs and removes the VM detour with the GSC component lifecycle.

Game and VM lifecycle

Replacement entries are only valid for the current script VM/game state. All
registered replacements are cleared during the script shutdown hook, before
the original shutdown routine continues. This is important because compiled
GSC code positions can become invalid after a game or map is shut down.

The cleanup runs every time the current game is shut down, so old replacement
functions do not carry over into a new game. Each new game starts with a clean
replacement table and can register its own mappings safely. Clearing the map
removes the old replacement registrations; it does not modify or delete the
original GSC functions.

Status

The implementation works perfectly in its intended use: functions register
correctly, calls are redirected through the VM to their replacements, invalid
arguments are rejected with a diagnostic, and all old replacement entries are
cleared when the game shuts down before the next game starts.

This keeps replaceFunc reliable across map/game transitions and prevents stale
function pointers from being reused by a later script VM instance.

[michaeloliverx]

Refactored some stuff, thanks!