* Update the arb filename parsing to account for underscores

* Generalize the locale searching algorithm

* Update filename and @@locale behavior to require them to match

After Dart VM change we are now required to use loadLibrary on an import whenever it is imported as deferred.

See: https://dart-review.googlesource.com/c/sdk/+/149613

* Fix breaking change introduced by gen_l10n output-dir option

* Add new output-dir option for gen_l10n tool

* Generate methods using template resources if they do not exist in other locales

* Added a flag to either output of messages that have not been translated with detail into a file, or display a summary on the terminal.

* Add integration test for fallback message usage

* Expose --header and --header-file arguments for gen_l10n

* unnecessary escapes fixes

* replace some strings with raw strings

* update regexp

* address review comments

[a11y] Make sure RenderFractionalTranslation updates its semantics after the translation field is set (#48985)

* Add currency formatting for l10n tool, fix positional vs named params

* Add preferred-supported-locales option to gen_l10n.dart executable

* Handle simple placeholders in plurals

* Handle Date plural placeholders

* Improve variable names

* Turn assert into exceptions, add tests

* Implement date parsing for the gen_l10n tool

* Add tests for sorting arbPathString, supportedLocales and supportedLanguageCodes alphabetically

* Plural arbPathStrings

* Factor out singleZhMessageArbFileString

* Make translations more accurate and generic

* Add tests to gen_l10n.dart tool

* Separate out LocalizationsGenerator class to improve testability of code

* Add testing dependencies to dev/tools

* Integrate dev/tools testing to flutter CI

* Restructure dev/tools folder for testing

* Fix license headers

This changes the publishing of archives so that it happens on the chrome_infra bots when they build a packaged branch instead of as part of the dev_roll process.

It uses the tagged version in the branch, and leaves the git repo that it clones checked out on the branch and hash used to build the package.

It updates metadata located at gs://flutter_infra/releases/releases_.json (where is one of macos, linux, or windows) once published, since it would be complex to do the proper locking to keep them all in one shared .json file safely.

A separate [change to the chrome_infra bots](https://chromium-review.googlesource.com/c/chromium/tools/build/+/902823) was made to instruct them to build packaged for the dev, beta, and release branches (but not master anymore).