BigQuery: ArrayQueryParameter.from_api_repr fails with STRUCT query parameter values

[tswast]

I encountered a system test error on the bigquery-b2 work when I modified some system tests to use QueryJob to pass in query parameters. The job resource that comes back cannot be parsed because of the query parameters in the query statistics.

The resource which is show the problem is this one:

    RESOURCE = {
        'parameterType': {
            'type': 'ARRAY',
            'arrayType': {
                'type': 'STRUCT',
                'structTypes': [
                    {
                        'name': 'name',
                        'type': {'type': 'STRING'}},
                    ,
                    {
                        'name': 'age',
                        'type': {'type': 'INT64'},
                    },
                ],
            },
        },
        'parameterValue': {
            'arrayValues': [
                {
                    'structValues': {
                        'name': {'value': 'Phred Phlyntstone'},
                        'age': {'value': '32'},
                    },
                },
                {
                    'structValues': {
                        'name': {
                            'value': 'Bharney Rhubbyl',
                        },
                        'age': {'value': '31'},
                    },
                },
            ],
        },
    }

I'm currently investigating a fix. Will make a PR to master rather than bigquery-b2 when ready because this issue will affect that branch too and I want a fix out possibly before Beta 2 is ready.