Add dart_skills_lint to dev/tool with test and update readme instructions for new skills authors

[reidbaker]

Add a static analysis linter for skills authors in flutter/flutter

I want to call out that this is adding a dependency on repo we control but is not yet available in pub.dev.

Update deps also had me fix an build error caused by updating build_runner.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• 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.

[gemini-code-assist]

Code Review

This pull request adds documentation for validating skills and introduces an automated validation test using the dart_skills_lint package. The review feedback suggests pinning the git dependency to a specific commit hash to ensure deterministic builds and improving test isolation by restoring the global logger level after the test completes.

[reidbaker]

Test failures appear to be from tip of tree. Will wait until the tree is green the sync and rerun cicd.

[jtmcdole]

There's a license missing:

The following file does not have the right license header for dart files:
  /b/s/w/ir/x/w/flutter/dev/tools/test/validate_skills_test.dart
The expected license header is:
// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

and the tools tests are failing

[bkonyi]

This change doesn't look like it was intended, or was it?

[reidbaker]

bad merge resolution that was required because head was broken. Fixed now.

[bkonyi]

I don't think we need to upgrade versions in the pubspecs to add the git dependency. If you revert those changes and run flutter update-packages --update-hashes that should be enough.

[reidbaker]

I don't think we need to upgrade versions in the pubspecs to add the git dependency. If you revert those changes and run flutter update-packages --update-hashes that should be enough.

FWIW I ran flutter update-packages because the test that failed lock file checking said that was the command to run. PR now only uses --update-hashes