rename local functions with _s

[pq]

rename local functions with _s

These will be flagged by the next linter release which updates non_constant_identifier_names to flag local functions.

See also: #664. (This has crept in since then.)

And:

• rename local functions with _s flutter#102615
• https://dart-review.googlesource.com/c/sdk/+/242391
• no_leading_underscores_for_local_identifiers doesn't complain about local functions dart-lang/linter#3360

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.

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[goderbauer]

LGTM

[pq]

As per #664 (comment), landing this in spite of persisting Golden tests issues.

[guidezpl]

The goldens were correct at HEAD (https:/flutter/gallery/actions/runs/2265454389), please revert those you included in this PR.

[pq]

So sorry! Those were included by accident. Will fix. 😬