[ENHANCEMENT] Add DEBUG_BUILD to Constants.

[AbnormalPoof]

Currently, there's no real way to detect whether or not the game is a debug build in HScript (MacroUtil doesn't work, so does basically anything that involves getting compiler defines), you COULD do something like this:

function isDebugBuild():Bool {
  return Constants.versionSuffix == ' PROTOTYPE';
}

However, this is unreliable since V-Slice forks can change the version suffix.

This PR adds a new boolean to Constants, DEBUG_BUILD. Which is basically self-explanatory, false if it's a release build, and true if it's debug (has the FEATURE_DEBUG_FUNCTIONS compiler flag).