add mechanism to batch hide/unhide items of a user's collection

[sabjorn]

To hide/unhide an item in a collection, each item has to be individually clicked on. The simplest form form of this feature would be to hide/unhide the whole collection at once.

A more elaborate mechanism would be to allow users to click on a checkbox for each item and run against that.

example code for hide/unhide:

fetch("https://bandcamp.com/api/collectionowner/1/hide_unhide_item", {
  "headers": {
    "accept": "*/*",
    "accept-language": "en-US,en;q=0.9,ar;q=0.8",
    "cache-control": "no-cache",
    "content-type": "application/json",
    "pragma": "no-cache",
    "priority": "u=1, i",
    "sec-ch-ua": "\"Chromium\";v=\"130\", \"Google Chrome\";v=\"130\", \"Not?A_Brand\";v=\"99\"",
    "sec-ch-ua-mobile": "?0",
    "sec-ch-ua-platform": "\"macOS\"",
    "sec-fetch-dest": "empty",
    "sec-fetch-mode": "cors",
    "sec-fetch-site": "same-origin",
    "x-requested-with": "XMLHttpRequest"
  },
  "referrer": "https://bandcamp.com/dataist",
  "referrerPolicy": "strict-origin-when-cross-origin",
  "body": "{\"fan_id\":896389,\"item_type\":\"track\",\"item_id\":2976775980,\"action\":\"unhide\",\"collection_index\":null,\"crumb\":\"|api/collectionowner/1/hide_unhide_item|1733202597|ch0AT2tBeFmbL/wH1mm77TFC2TI=\"}",
  "method": "POST",
  "mode": "cors",
  "credentials": "include"
});```

notice the 'action' is `unhide` -- hide is `hide`