Random NPCs have the same starting skills and proficiencies as the average new character

[RenechCDDA]

Summary

Balance "Random NPCs have the same starting skills and proficiencies as the average new character"

Purpose of change

Players got buffed, but our NPCs are still churls without driver's licenses?!

Maintainability for NPCs is poor, let's fix that.

Describe the solution

-Fix a pretty bad bug with bad variable handling. Proficiencies and a few other values were being set by the passed argument type... this was in all cases npc_class_id::NULL_ID(). myclass was set by randomizing from a common NPC class

Cataclysm-DDA/src/npc.cpp

Line 605 in 9640195

myclass = npc_class::random_common();

...but myclass was not used to determine the resulting proficiency/other values. Always the empty type. This meant that if the new NPC randomized into a class with proficiencies... it didn't get the proficiencies, because the null type has no proficiencies. Enormous sigh.

-Apply the default starting character background to NPCs if they are randomly generated (unique classes can still do whatever they want). Add a special modifier so that the skills gained from these backgrounds don't interfere with existing skill definitions, they only raise the bare minimum. Basically this means random NPCs start proficient in driving and home cooking with very basic skill levels, just like the player character. NPCs have learned how to drive! Hooray! Not yet.

Because this draws form the same starting background as the player character it should automatically track any future changes without any specific handling. Maintainability!

-In the interests of maintainability and ease of contributing, make their proficiency learning recursive instead of simply failing if a pre-req is missing. This means that if our proficiency trees change in the future (by adding a new proficiency or removing an existing link into a new tree), contributors will not to go through and laboriously re-verify every NPC class' proficiencies. They simply define the top-level ones they should have, and all the pre-reqs fill in from there.

Describe alternatives you've considered

Completely combining professions and NPC classes? That is a suggestion which has been put forth before...

common is maybe not the optimal way to determine if the adult_basic_background should be applied, but bumping that out to a new json value is incredibly simple if any problems arise.

Testing

Many newly generated NPCs, all of which had driving, food prep, and minimum skill levels. Here's one:

Additional context