make u_spawn_item to support the item group whose subtype is collection

[PipeYume]

Summary

Features "make u_spawn_item to support the item group whose subtype is collection"

Purpose of change

Close #71000

Describe the solution

Modify the receive_item function which is used by set_spawn_item and set_u_buy_item.

If the use_item_group is true, then it will call the item_group::items_from function and create one item (distribution) or collection of items (collection) from that item group, then do the same things as previous. (The popup message will be shown once)

Since the count and containter are defined in item group, "count" and "container" options of "u_spawn_item" will be ignored.

Describe alternatives you've considered

Testing

[
  {
    "id": "test_EOC_spawn_item_group_collection",
    "type": "item_group",
    "//": "This is for testing u_spawn_item",
    "subtype": "collection",
    "entries": [
      { "item": "bodysuit_lycra", "variant": "superhero_suit_purple" },
      { "item": "mask_bal", "prob": 50 },
      { "item": "long_patchwork_scarf", "count": [ 2, 4 ] },
      { "item": "rock", "charges": [ 2, 4 ] }
    ]
  },
  {
    "id": "test_EOC_spawn_item_group_distribution",
    "type": "item_group",
    "//": "This is for testing u_spawn_item",
    "subtype": "distribution",
    "entries": [
      { "item": "bodysuit_lycra", "variant": "superhero_suit_purple" },
      { "item": "mask_bal", "prob": 50 },
      { "item": "long_patchwork_scarf", "count": [ 2, 4 ] },
      { "item": "rock", "charges": [ 2, 4 ] }
    ]
  },
  {
    "type": "effect_on_condition",
    "id": "EOC_spawn_item_group_test",
    "//": "tests for spawning item group (collection / distribution). Alpha and beta talker is for showing the popup message",
    "effect": [
      { "message": "collection: ", "popup": true },
      {
        "run_eoc_with": {
          "id": "_EOC_spawn_item_group_test_collection",
          "effect": {
            "u_spawn_item": "test_EOC_spawn_item_group_collection",
            "use_item_group": true,
            "force_equip": true,
            "flags": [ "UNBREAKABLE" ]
          }
        },
        "alpha_talker": "avatar",
        "beta_talker": "avatar"
      },
      { "message": "distribution: ", "popup": true },
      {
        "run_eoc_with": {
          "id": "_EOC_spawn_item_group_test_distribution",
          "effect": {
            "u_spawn_item": "test_EOC_spawn_item_group_distribution",
            "use_item_group": true,
            "force_equip": true,
            "flags": [ "UNBREAKABLE" ]
          }
        },
        "alpha_talker": "avatar",
        "beta_talker": "avatar"
      }
    ]
  }
]

Additional context