Merge flutter/plugins into flutter/packages #113764

Tracking bug for implementing https://flutter.dev/go/flutter-plugins-repo-migration

• Pre-align Dockerfile
• Pre-align .cirrus.yaml
• Pre-align .ci.yaml, .ci/scripts, and .ci/targets
  • Including making sure the generic recipes driving them are aligned after recent drift
• Pre-align install_chromium.sh
• Pre-align analysis_options.yaml
• Pre-test a migration pattern for in-progress PRs, and write up a wiki page clearly documenting the steps.
  • Draft page here.
• Pre-test a history graft locally with git-filter-repo
• Move repo tooling from flutter/plugins to flutter/packcages
• Stop the flutter/flutter -> flutter/plugins roller
• Update flutter/plugins README and CONTRIBUTING
• Close all PRs in flutter/plugins with an explanation
• Re-validate that pre-aligned configurations still match
• Archive flutter/plugins
• Update repository tooling to enforce that the ‘repository’ entry in pubspec.yaml points to flutter/packages, and fix all of the violations.
• Land the PR to graft flutter/plugins history into flutter/packages
• Update docs (flutter/packages docs, Flutter wiki) referencing flutter/packages
• Update the flutter/flutter CI analysis of flutter/plugins to instead analyze flutter/packages
• Update the Dart CI analysis of flutter/plugins to instead analyze flutter/packages
• Fully turn down the flutter/flutter → flutter/plugins rollers
• Update flutter/packages README, especially the package table
• Update flutter/packages CONTRIBUTING docs
• Update internal gardening docs