Send empty privateVisibilityConfig network array

[modular-magician]

fixes hashicorp/terraform-provider-google#6973

The api only removes the privateVisibilityConfig block when sending an empty networks array like so:

  "privateVisibilityConfig": {
    "networks": []
  }

Added a custom expander to do this. Using a custom expander on the parent field removed the expanders for the subfields, so I included the subfield expanders in the template. This makes the custom expander looks excessive, but generates small downstream diffs.

Release Note Template for Downstream PRs (will be copied)

dns: fixed an issue where `google_dns_managed_zone` would not remove `private_visibility_config` on updates

Derived from GoogleCloudPlatform/magic-modules#3865