npctalk: add dialogue effects to give items to NPCs

[mlangsdorf]

Summary

SUMMARY: Infrastructure "npctalk: add dialogue effects to give items to NPCs"

Purpose of change

Create dialogue effects that let the character give items to NPCs to hold or to use, and migrate the dialogue responses that used to implement giving items to NPCs into JSON.

This will hopefully resolve an issue reported by @A.Fulcrum where asking an NPC to train when the NPC was thirsty would be spawn the dialogue window to give the NPC something, but only under certain ill-defined circumstances.

Describe the solution

Add dialogue effects for give_npc_item and give_npc_item_to_use that allow the player to give an item to a NPC. If the NPC rejects the item, the NPC sets a reason which can be used in future dynamic lines by the NPC.

Describe alternatives you've considered

I could debug A.Fulcrum's actual issue, but that sounds difficult and tedious, while doing this means there are even more dialogue options in JSON and less in C++.

[mlangsdorf]

jenkins rebuild