Message enums are included in file_enums

[pstavirs]

Enums nested inside a message definition should be included as part of a new key "message_enums" instead of being included at the top file level "file_enums".

enum FileEnum {
    A = 1;
    B = 2;
}

message MyMessage {
    enum MessageEnum {
        C = 3;
        D = 4;
    }
}

[
    {
        "file_description": "",
        "file_enums": [
            {
                "enum_description": "",
                "enum_full_name": "FileEnum",
                "enum_long_name": "FileEnum",
                "enum_name": "FileEnum",
                "enum_values": [
                    {
                        "value_description": "",
                        "value_name": "A",
                        "value_number": 1
                    },
                    {
                        "value_description": "",
                        "value_name": "B",
                        "value_number": 2
                    }
                ]
            },
            {
                "enum_description": "",
                "enum_full_name": "MyMessage.MessageEnum",
                "enum_long_name": "MyMessage.MessageEnum",
                "enum_name": "MessageEnum",
                "enum_values": [
                    {
                        "value_description": "",
                        "value_name": "C",
                        "value_number": 3
                    },
                    {
                        "value_description": "",
                        "value_name": "D",
                        "value_number": 4
                    }
                ]
            }
        ],
        "file_extensions": [
        ],
        "file_has_extensions": false,
        "file_has_services": false,
        "file_messages": [
            {
                "message_description": "",
                "message_extensions": [
                ],
                "message_fields": [
                ],
                "message_full_name": "MyMessage",
                "message_has_extensions": false,
                "message_long_name": "MyMessage",
                "message_name": "MyMessage"
            }
        ],
        "file_name": "test.proto",
        "file_package": "",
        "file_services": [
        ]
    }
]