Monster vision enchantment and evaluation

[GuardianDll]

Summary

None

Purpose of change

Request from discord

Describe the solution

Add monster enchantment, that affects monster vision range
Update vision_range_eval to return vision range of monster also

Testing

  {
    "type": "effect_on_condition",
    "id": "EOC_TEST_APPLY_EFFECT",
    "eoc_type": "EVENT",
    "required_event": "character_melee_attacks_monster",
    "effect": [
      { "math": [ "_a", "=", "n_vision_range()" ] },
      { "npc_add_effect": "effect_test_test", "duration": 9999 },
      { "u_message": "monster vision range: <context_val:a>" }
    ]
  },
  {
    "id": "effect_test_test",
    "type": "effect_type",
    "name": [ "AAAAA" ],
    "desc": [ "AAAAA." ],
    "rating": "good",
    "show_intensity": true,
    "enchantments": [ { "values": [ { "value": "VISION_RANGE", "add": 5 } ] } ]
  }

"enchantments": [ { "values": [ { "value": "VISION_RANGE", "multiply": 0.5 } ] } ]

"enchantments": [ { "values": [ { "value": "VISION_RANGE", "multiply": -0.5 } ] } ]