Updates to style guide

[Piinks]

Companion PR: #181934
Design doc: Flutter Style Updates
Closes #180607
Also closing #172296

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 and followed the Flutter Style Guide, including Features we expect every widget to implement.
• 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.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

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[gemini-code-assist]

Code Review

This pull request updates the Flutter repository style guide. Key changes include modifying the test setup guidance to recommend addTearDown, restructuring the advice on test file organization, and removing several sections related to pumpAndSettle, anonymous parameter names, and the use of arrow (=>) syntax. My review identifies two potential issues: the removal of the pumpAndSettle guidance could lead to the loss of a valuable best practice, and the removal of the section on anonymous parameter names introduces an inconsistency with another part of the document.

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docs/contributing/Style-guide-for-Flutter-repo.md (1050-1054)

The section advising against the use of pumpAndSettle has been removed. This guidance is valuable for preventing brittle tests, and its removal could be a loss. If this was unintentional, please consider restoring it. If intentional, it would be helpful to understand the rationale, as the reasons for avoiding pumpAndSettle are still valid according to its API documentation.

docs/contributing/Style-guide-for-Flutter-repo.md (1078-1086)

The removal of the 'Avoid anonymous parameter names' section is a good step towards aligning with the general Dart style guide. However, it introduces an inconsistency. A paragraph in the 'Naming rules for typedefs and function variables' section still advises to 'give the type and names of the arguments anyway' even when they are ignored. To maintain consistency, this conflicting guidance should also be addressed, either by updating or removing it.

[Piinks]

#181880 was well-timed, I incorporated it here as it aligned well with where we arrived at here to update.

[chunhtai]

mostly LGTM, just left a comment

[loic-sharma]

Thanks!

[chunhtai]

LGTM

[justinmc]

LGTM 👍

[justinmc]

Do we still have a preference for things like this onTapUp, or either way is fine? I understand the need for anonymous parameter names in switch statements, but I always liked this for readability:

onTapUp: (TapUpDetails details) {...

I've seen a lot of places in the codebase that don't follow this though, so I'm fine giving it up if others want to, or if there's no good way to distinguish this and switch.

[Piinks]

In the forum, we discussed that if the parameter is anonymous, it is not being used in the callback, and is thus not really relevant. Feedback supported allowing anonymous parameters in this case.