fix: ignore comments apply to trailing commas

[dsherret]

Closes #9

A property or array element with an ignore comment (ex. // dprint-ignore) now keeps its trailing comma as written. Before, trailingCommas still added or removed the comma, so this was changed when using never, or jsonc on a .json file (which is how Deno hits it):

{
  "tasks": {
    // dprint-ignore
    "foo": "echo bar",
  }
}

When the last node is ignored, its trailing comma is now handled as maintain. Like maintain, the kept comma only prints when the object or array is multi-line.

Tests: specs for never, always, and jsonc on a .json file, covering object properties and array elements.

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