* [gen_l10n] Support string list as preferred-supported-locales, as documented.

* [gen_l10n] Convert preferredSupportedLocale to a list of strings. 

* [gen_l10n] Accept a multi option instead of a json string in the command line.

* synthetic packages by default in gen_l10n tool

* Refactor default path for synthetic package

* Remove unused import

* Code cleanup

* Further improvements to help text

* Refactor synthetic package path

* Remove newlines

* Test cleanup

* clean up logic in inputs and outputs list function

* Update l10n.yaml usage

* only add option if value is non-null

* Update stocks app as proof of concept for synthetic package usage

* Address nits

* print pubspec contents

* add print statements

* Do not allow null value for useSyntheticPackage

* +

* +

* +

* +

* Cleanup

* Add test

* Fix text

* Dont parse pubspec directly

* Test using context

* WIP: generate synthetic packages on pub get -- needs tests

* Allow null value

* Update null handling

* Refactor to properly handle null case

* Fix yamlMap condition

* Fix yaml node for real

* WIP: struggling to write tests

* WIP - take absolute path as an option

* Add tests

* Use environment project directory for synthetic package generation pathway

* Fix typo

* Improve help text

* Update defaults

* Remove unauthorized path import

* Fix pathing issues at synthetic package generation

* Fix typo in test

* Use path.join so projectDir matches up based on OS

* Fix Windows pathing in test

* Remove unnecessary replaceApp code for projectDir.path

* Use globals.fs.currentDirectory.path in resident_runner_test.dart

* Fix merge conflict

* Add test to ensure that synthetic package is generated on pub get

* Fix resident_runner_test.dart tests

* Fix tests

* Use package:file instead of dart:io

* WIP - exploration

* Remove synthetic package use from stocks example

* Update integration test to not use synthetic packages

* Remove trailing whitespace

* flutter pub get runs synth package generation

* Remove more print statements

* Add license header

* WIP - minimally working pub.get

* Use own MockBuildSystem

* Modify test and implementation to be a little cleaner

* Fix flutter pub get invocation

* Use synthetic packages in stocks app

* Revert "Use synthetic packages in stocks app"

This reverts commit 45bf24903c3d4a2a5fd5481d7d6bc36c4a348703.

* Add environment and buildSystem params to flutter test

* Address code review feedback

* +

* Isolate codegen into its own API

* Fix imports

* Slight refactor

* Add one more test for no l10n.yaml file

* Remove unneeded mock class and import in pub_get_test.dart

* More code review feedback

* Remove unnecessary imports

* Remove `return await`s that I missed

* use arrow functions instead

* 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

* [gen_l10n] Add scriptCode handling

* Fix suppportedLocales list

* Refactor integration tests for gen_l10n tool to catch exceptions

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

* 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

This reverts commit c235998a.

* 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

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs