Fixes before publish

[mosuem]

License files and running dart pub upgrade --major-versions

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• See our contributor guide for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
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[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:messages_serializer	0.1.0	ready to publish	messages_serializer-v0.1.0
package:messages_builder	0.1.0	ready to publish	messages_builder-v0.1.0
package:messages_shrinker	0.1.0	ready to publish	messages_shrinker-v0.1.0
package:intl_translation	0.19.0-dev	ready to publish	intl_translation-v0.19.0-dev
package:intl	0.19.0-dev	ready to publish	intl-v0.19.0-dev
package:messages	0.1.0	ready to publish	messages-v0.1.0
package:messages_deserializer	0.1.0	ready to publish	messages_deserializer-v0.1.0
package:intl4x	0.7.0	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.