Cost allowance for "give_equipment"

[dseguin]

Summary

None

Purpose of change

Fixes #14619.
Requesting an item from an NPC gives you credit with that NPC, as an unintentional side-effect of "add_debt" and "give_equipment".

Describe the solution

(This solution is derived from a comment on #52818 (comment))

Instead of giving the player credit with the NPC, use a temporary allowance for the cost of the item:

"effect": {
  "give_equipment": {
    "allowance": [ [ "TRUST", 1 ], [ "VALUE", 3 ], [ "ALTRUISM", 2 ], [ "TOTAL", 300 ] ]
  }
}

The allowance accepts either a flat integer, or a group of trial modifiers similar to "add_debt". This allows talk_function::give_equipment_allowance to pull the item cost from the allowance (as well as any existing debt with the NPC), and ensures that none the leftover credit is added to the NPC's debt.

The regular "add_debt" and "give_equipment" (without allowance) effects remain the same, so they can still be used like before.

Describe alternatives you've considered

Testing

1. Before asking the NPC for an item, player has zero credit/debt:

2. Requesting an item from the NPC (using option a, since it provides an allowance):

3. Afterwards, player still has zero credit/debt with the NPC:

Additional context

wow, that's a really old bug :P

[Leland]

thanks for solving ancient stuff! kudos