Dialogue: JSON fields for displaying hidden responses

[ShnitzelX2]

Summary

Features "dialogue: JSON fields for displaying hidden responses"

Purpose of change

Closes #56925

Describe the solution

Fully implemented as described. There are three new JSON fields for responses, and debug support for showing all hidden responses. Quoting the docs I updated for an easy summary:

show_condition

An optional key that, if defined and evaluates to true, will allow the response to be displayed even if it has a condition evaluating false. The response still will not be selectable if its condition is false, unless debug mode is ON. Cannot be defined if show_always: true. Note: do not confuse show_condition with condition. Empty by default.

show_always

Shorthand for "show_condition": takes a boolean instead of a condition. False by default.

show_reason

An optional key that, if defined, will append its contents to the end of a response displayed because of show_always or show_condition.

Also fixes an apparent segfault bug from #76681

Describe alternatives you've considered

#76792 was my initial attempt and broke npc_talk_test.cpp, which was not ideal. This PR is smaller and less convoluted, and doesn't break any tests.

Testing

I wrote some new talk_topic test cases for show_always, show_reason, and show_conditional, made sure they work.
I also made sure that talking to NPCs, Rubik, and Hub01 was normal. Made sure my last debug PR was compatible with this one; as with that PR, this functionality is not exhaustively tested by any means.

Additional context

Talking to Rubik, all responses shown

toggling responses off

An example of show_condition/show_reason

[PatrikLundell]

I assume the show_always case doesn't actually disable access to the option unless debug_mode is on, but rather disables access only if conditions evaluate to false and debug mode is off. Thus, the text may need some adjustment.

Ditto for show_condition.