[Java] Support for textual JSON schema representation (was: JSON representation of pojo.Schema is incompatible with flatbuffers JSON generated via C++ API)

const void* schemaBytes;

std::string fbsSchemaFile;    
flatbuffers::LoadFile("/path/to/Schema.fbs", false, &fbsSchemaFile);

flatbuffers::Parser parser;
parser.Parse(fbsSchemaFile.c_str());

std::string json;
flatbuffers::GenerateTextFromTable(parser, schemaBytes, "org.apache.arrow.flatbuf.Schema", &json);

return json;

String json; // Read from file.
Schema.fromJSON(json);

{
  fields: [
    {
      name: "cc_call_center_sk",
      type_type: "Int",
      type: {
        bitWidth: 32,
        is_signed: true
      },
      children: [

      ],
      custom_metadata: [
        {
          key: "metadata",
          value: "some_metadata"
        }
      ]
    },
  ],
  custom_metadata: [
    {
      key: "metadata",
      value: "some_metadata"
    }
  ]
}

{
  "fields" : [ {
    "name" : "cc_call_center_sk",
    "nullable" : true,
    "type" : {
      "name" : "int",
      "bitWidth" : 32,
      "isSigned" : true
    },
    "children" : [ ],
    "metadata" : [ {
      "value" : "some_metadata",
      "key" : "metadata"
    } ]
  } ],
  "metadata" : [ {
    "value" : "some_metadata",
    "key" : "metadata"
  } ]
}