Load sound-triggered traps with more safety

[RenechCDDA]

Summary

None

Purpose of change

An enterprising modder was trying to use the character_triggers_trap event for eoc scripting and found out that sound_detect traps didn't actually require a sound threshold to trigger.

Further investigation found that sound_detect is a (rather confusingly named!) vestigial trapfunc used only for initial testing sound-triggered traps. Sound-triggered traps definitely work, and we have an existing trap type (tr_dormant_zombie) which uses them.

Describe the solution

-Delete sound_detect trapfunc and associated trap. These were not encounterable outside of the debug menu and the trapfunc itself did nothing besides verify its function, so this shouldn't impact mods. No migration or save handling was provided (if a save does have them it will delete the trap on load after throwing an error about being unable to find it).

-Add some safety to our loading by throwing errors when invalid sound_thresholds are detected.

-Add dummy_trap function which always counts as triggering when called (thus calling the event bus) for our enterprising modder.
--I had originally added a dummy trap to traps.json as a sort of in-json documentation, but on reflection I found it hypocritical to be adding an unused trap in the same PR I was removing one. Maybe we should separate out the traps documentation from json_info.md and list(just list, not describe) the hardcoded trapfuncs so people can reasonably know they exist?

Describe alternatives you've considered

Actual documentation for traps?

Unit test for sound-triggered traps?

Testing

Game loads, dummy trap calls event bus when stepped on

Additional context

  {
    "type": "trap",
    "id": "tr_dummy_always_triggers",
    "name": "noise test trap",
    "color": "light_cyan",
    "symbol": "_",
    "visibility": 0,
    "avoidance": 99,
    "difficulty": 99,
    "action": "dummy_trap"
  },