Formatter support for sorting includes

[DartBot]

This issue was originally filed by tonyg@chromium.org

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It'd be really nice if the formatter sorted includes according to https://www.dartlang.org/articles/style-guide/#ordering (or exposed an option to do so if that's controversial).

In my experience writing Dart for the Mojo project, the formatter takes away 99% of thinking about the style guide. Import alphabetization is the main place I still find myself having to make stylistic code review comments.

[DartBot]

This comment was originally written by @zoechi

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I think formatter issues should be created in the github.com/dart-lang/dart_style repo

[DartBot]

This comment was originally written by @seaneagan

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#57172

[lrhn]

Added MovedToGithub label.