feat: accept TableListItem where TableReference is accepted

[steffnay]

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[tswast]

Looks like we need to either update the test_get_iam_policy_w_invalid_table test to look for ValueError or update _parse_3_part_id to raise TypeError.

Based on https://docs.python.org/3/library/exceptions.html#TypeError, I think ValueError is more accurate.

________________ TestClient.test_get_iam_policy_w_invalid_table ________________

self = <tests.unit.test_client.TestClient testMethod=test_get_iam_policy_w_invalid_table>

    def test_get_iam_policy_w_invalid_table(self):
        creds = _make_credentials()
        http = object()
        client = self._make_one(project=self.PROJECT, credentials=creds, _http=http)

        table_resource_string = "projects/{}/datasets/{}/tables/{}".format(
            self.PROJECT, self.DS_ID, self.TABLE_ID,
        )

        with self.assertRaises(TypeError):
>           client.get_iam_policy(table_resource_string)

tests/unit/test_client.py:1558:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
google/cloud/bigquery/client.py:813: in get_iam_policy
    table = _table_arg_to_table_ref(table, default_project=self.project)
google/cloud/bigquery/table.py:2666: in _table_arg_to_table_ref
    value = TableReference.from_string(value, default_project=default_project)
google/cloud/bigquery/table.py:252: in from_string
    ) = _helpers._parse_3_part_id(
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    def _parse_3_part_id(full_id, default_project=None, property_name="table_id"):
        output_project_id = default_project
        output_dataset_id = None
        output_resource_id = None
        parts = _split_id(full_id)

        if len(parts) != 2 and len(parts) != 3:
>           raise ValueError(
                "{property_name} must be a fully-qualified ID in "
                'standard SQL format, e.g., "project.dataset.{property_name}", '
                "got {}".format(full_id, property_name=property_name)
            )
E           ValueError: table_id must be a fully-qualified ID in standard SQL format, e.g., "project.dataset.table_id", got projects/PROJECT/datasets/DATASET_ID/tables/TABLE_ID

google/cloud/bigquery/_helpers.py:848: ValueError

[tswast]

Need unit test that covers this. Possibly this if statement can be deleted if _table_arg_to_table_ref already throws?

[tswast]

Line not covered in unit tests

[steffnay]

Ah, got it! Thanks!

[tswast]

Line not covered in unit tests