Standard library function `write_json` does prohibited serialization of integer keys

[stxue1]

The WDL spec states that write_json cannot serialize a map with integer keys.

  Pair[Int, Map[Int, String]] x = (1, {2: "hello"})
  # this fails with an error - Map with Int keys is not serializable
  File f = write_json(x)

MiniWDL will coerce Int to String, meaning the map above is serializable from MiniWDL's perspective:

version 1.1

workflow write_json_fail {
  Pair[Int, Map[Int, String]] x = (1, {2: "hello"})
  # this fails with an error - Map with Int keys is not serializable
  File f = write_json(x)
  output {
    File out = f
  }
}

2024-07-02 18:25:13.770 wdl.w:write_json_fail workflow start :: name: "write_json_fail", source: "/home/heaucques/Documents/wdl-conformance-tests/unit_tests/write_json_fail.wdl", line: 3, column: 1, dir: "/home/heaucques/Documents/wdl-conformance-tests/20240702_182513_write_json_fail"
2024-07-02 18:25:13.772 wdl.w:write_json_fail miniwdl :: version: "v1.12.0", uname: "Linux pop-os 6.9.3-76060903-generic #202405300957~1718348209~22.04~7817b67 SMP PREEMPT_DYNAMIC Mon J x86_64"
2024-07-02 18:25:13.786 wdl.w:write_json_fail done
{
  "dir": "/home/heaucques/Documents/wdl-conformance-tests/20240702_182513_write_json_fail",
  "outputs": {
    "write_json_fail.out": "/home/heaucques/Documents/wdl-conformance-tests/20240702_182513_write_json_fail/out/out/tmpctwkrlfx"
  }
}

$ cat /home/heaucques/Documents/wdl-conformance-tests/20240702_182513_write_json_fail/out/out/tmpctwkrlfx
{"left": 1, "right": {"2": "hello"}}