Added failing test for serialization

[aaroncox]

The authorized_by field during serialization is getting screwed up, and this is affecting iOS users who try to use any action in the system contract that leverages it.

This field appears to be a binary extension, judging by the $ at the end of the type:

{
    "name": "deleteauth",
    "base": "",
    "fields": [
        {
            "name": "account",
            "type": "name"
        },
        {
            "name": "permission",
            "type": "name"
        },
        {
            "name": "authorized_by",
            "type": "name$"
        }
    ]
}

When dealing with any of these actions that use it (unlinkauth, linkauth, deleteauth, etc), the result in Anchor is as follows. The transaction that is getting signed has messed up data, causing the signature to be invalid.

I believe we need to fix the serializer here, then update Anchor (iOS), in order to resolve this bug.