Add registry for patrol packages

[piotruela]

This PR add testing 3 packages that together form the Patrol testing tool:

• patrol_cli
• patrol
• patrol_finders

They relies on multiple dependencies pinned by the Flutter SDK, most importantly on test_api.

Even though the tests only consist of running flutter analyze and flutter test in all three packages, the entire process takes ~30 minutes on my local machine. I could probably break this script into 3 separate ones so that each takes less than 15 minutes. If I should do that, please let me know.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[piotruela]

Replaced by #420