[CQ] (tall-style) dart re-format

[pq]

Modernize dart files w/ a fresh formatting (to tall-style).

To avoid future churn, we might consider formatting validation in a test or a presubmit.

We might consider similar for sorting (as we do in the analyzer code base).

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.

[pq]

Picked up in #7920