add enum/map support to zjson

[mccanne]

After the zjson branch is merged, we need to add zjson support for enum and map.

[philrz]

@mccanne: It looks like this one is already taken carte of. Starting with zq commit fa68b5f (associated with #1394 where enum and map types were added for ZNG in general) I can output both enum and map in zjson format. Anything else left to do?

$ zq -version
Version: v0.22.0-25-gfa68b5f

$ cat enum.tzng 
#0:record[e:enum[int32,foo:[1],bar:[2],baz:[4]]]
0:[0;]
0:[1;]
0:[2;]

$ zq -f zjson enum.tzng | jq .
{
  "id": 24,
  "schema": {
    "of": [
      {
        "name": "e",
        "of": [
          {
            "type": "int32"
          },
          {
            "name": "foo",
            "value": "1"
          },
          {
            "name": "bar",
            "value": "2"
          },
          {
            "name": "baz",
            "value": "4"
          }
        ],
        "type": "enum"
      }
    ],
    "type": "record"
  },
  "values": [
    "0"
  ]
}
{
  "id": 24,
  "values": [
    "1"
  ]
}
{
  "id": 24,
  "values": [
    "2"
  ]
}

$ cat map.tzng 
#0:record[m:map[string,int32]]
0:[[a;1;b;2;c;3;]]

$ zq -f zjson map.tzng | jq .
{
  "id": 24,
  "schema": {
    "of": [
      {
        "name": "m",
        "of": [
          "string",
          "int32"
        ],
        "type": "map"
      }
    ],
    "type": "record"
  },
  "values": [
    [
      "a",
      "1",
      "b",
      "2",
      "c",
      "3"
    ]
  ]
}

[nwt]

Done in #1394.