Standardize Copyrights: Chromium->Flutter

[stuartmorgan-g]

Description

In all copyright messages (and in the Xcode project organization name) standardize on "The Flutter Authors", adding "The Chromium Authors" to the Flutter AUTHORS list. This reduces inconsistency in the copyright lines in this repository, moving closer to a single consistent copyright+license (as in flutter/engine and flutter/flutter)

Updates the validation script to no longer accept "The Chromium Authors" or "the Chromium project authors" in first-party code.

Related Issues

flutter/flutter#78448

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

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• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[stuartmorgan-g]

Per feedback from @Hixie I believe this is blocked on adding AUTHORS files to every single plugin; I'm not going to have time to get to that anytime soon, so closing.