jsondoclint: Check that ID lists don't have duplicates

[aDotInTheVoid]

If the json output has duplicated IDs in a list, like

  "index": {
    "0:0:1588": {
      "crate_id": 0,
      "docs": null,
      "id": "0:0:1588",
      "inner": {
        "is_crate": true,
        "is_stripped": false,
        "items": [
          "0:1:1582",
          "0:4-0:2:1584",
          "0:4-0:3:1584",
          "0:4-0:2:1584",
          "0:4-0:3:1584",
          "0:5-0:2:1584",
          "0:5-0:3:1584",
          "0:5-0:2:1584",
          "0:5-0:3:1584"
        ]
      },
      "kind": "module",
      "name": "same_name_different_types"
    },

Then jsondoclint should probably catch this, as it indicates a bug.

Originally posted by @aDotInTheVoid in #107766 (comment)