Refactor QueryJob.query to read from resource dictionary (#7763)
Refactor QueryJob.query to read from resource dictionary (#7763)

This explicitly documents the QueryJob.query property and also aligns it
with the other resource properties in the BigQuery client.
tseaver/google-cloud-python,tswast/google-cloud-python,tseaver/google-cloud-python,googleapis/google-cloud-python,googleapis/google-cloud-python,tswast/google-cloud-python,GoogleCloudPlatform/gcloud-python,tseaver/google-cloud-python,tswast/google-cloud-python,GoogleCloudPlatform/gcloud-python