Adopt AEP-180: Backwards Compatibility

[rambleraptor]

🍱 Types of changes

What types of changes does your code introduce to AEP? Put an x in the boxes that apply

• [x] Migrated from google.aip.dev

📋 Your checklist for this pull request

Please review the AEP Style and Guidance for contributing to this repository.

General

• [x] Basic Guidance is met.
• [x] Ensure that your PR references AEPs correctly.
• [x] My code has been formatted (usually prettier -w .)

Additional checklist for a new AEP

Fixes #8

💝 Thank you!

[rofrankel]

Maybe ask Jon Skeet for a review as well.