Add ResourceRefs for Compute Route.

[rileykarson]

We were failing some tests due to self link stability, turns out the resources weren't ResourceRefs because some old TODOs weren't completed.

Remove the reference to Gateway being added to MM because to my best knowledge that is not a GCP resource- only default-internet-gateway can be configured.

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[all]

[terraform]

Fix self link stability issues in google_compute_route

[terraform-beta]

[ansible]

[inspec]

[rileykarson]

@ndmckinley for general review + @rambleraptor for Ansible

[nat-henderson]

LGTM + tf downstreams

[rileykarson]

Historical Reference: I had to do a rebase/force push because #1123 made one of the changes but not the other and made that change in a slightly different way (I rearranged the input variable to be above description).

I'd merged my downstreams, then #1123's downstreams + upstream were merged before my upstream was merged. There should be no or minimal downstream changes.

[modular-magician]

I am a robot that works on MagicModules PRs!

I built this PR into one or more PRs on other repositories, and when those are closed, this PR will also be merged and closed.
depends: hashicorp/terraform-provider-google-beta#316
depends: hashicorp/terraform-provider-google#2805
depends: modular-magician/inspec-gcp#52

[rileykarson]

Closing out all the downstreams and merging, we suspect they were all generated in a short window (~90s) where PRs aren't reconciled correctly.