Random NPC classes can define weighted chance of spawning

[RenechCDDA]

Summary

Infrastructure "Random NPC classes can define weighted chance of spawning, relative to other random NPC classes"

Purpose of change

Multiple contributors requested this feature on the development discord. It makes sense - not every randomly spawnable class should be just as common as each other.

Describe the solution

Add a weighting variable, put the classes in a weighted list, pick from the list. Uses existing RNG functions - nothing new or fancy here. Existing classes without this variable defined will all have the same weight - 1.0, and will work exactly the same as before. If no weights are added, then the weight of each is 1.0, and the chances for a particular NPC class to roll is exactly the same as before.

Describe alternatives you've considered

Full support for conditions and math, so that the chance could be dynamic based on post-cataclysm time or other variables 😈

...That's a lot more effort though.

Testing

Game correctly errors when weighting is defined but class cannot spawn

Locally set the "Operator" class to 500 weight. Spawned about 10 NPCs after starting a new game. Got one doctor, the rest were operators. Quite the difference.

Additional context