Firewall case insensitive protocol

[slevenick]

Add diff suppress and update hash function to compare protocol insensitively for firewall rules

Fixes hashicorp/terraform-provider-google#4458

Release Note for Downstream PRs (will be copied)

`google_compute_firewall` does not show a diff if allowed or denied rules are specified with uppercase protocol values

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
I see that this PR has already had some downstream PRs generated. Any open downstreams are already updated to your most recent commit, 64d04a6.

Pull request statuses

No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I built this PR into one or more new PRs on other repositories, and when those are closed, this PR will also be merged and closed.
depends: hashicorp/terraform-provider-google-beta#1144
depends: GoogleCloudPlatform/terraform-google-conversion#203
depends: hashicorp/terraform-provider-google#4467

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
I see that this PR has already had some downstream PRs generated. Any open downstreams are already updated to your most recent commit, 17a1c79.

Pull request statuses

terraform-provider-google-beta already has an open PR.
terraform-google-conversion already has an open PR.
terraform-provider-google already has an open PR.
No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I didn't open any new pull requests because of this PR.