Adding support for using the Frontend Server with the Legacy/DDC modu…

[Markzipan]

This change adds a Frontend Server + Legacy module system strategy provider and adds some additional logic to the legacy bootstrapper. This logic interfaces with some of the API in dart_library.js as well as in the bootstrapper itself.

This is part of a greater effort to deprecate the AMD module system: dart-lang/sdk#52361

[Markzipan]

@annagrin @elliette Can you all point me to some places where I can add/plumb through tests + changelog/versioning details?

[annagrin]

Thanks Mark!

• please update the change log similar to in https://github.com/dart-lang/webdev/blob/master/dwds/CHANGELOG.md?plain=1#L2 (you can also see other PRs for examples).

• since you didn't change the API you don't need to update a version, so you can just add to the current version changelog

• This can be done in a separate PR if needed: please add a test option in context.dart for module format that allows to use the new strategy with the frontend server compilation mode and add a test (you can just copy and modify tests/frontend_server_evaluate_sound_test.dart).

[annagrin]

Thanks Mark, I left some comments.

[Markzipan]

Thanks Anna! Comments addressed + CHANGELOG entry added. I can land the tests in a followup.

[annagrin]

LGTM!