Support annotations on unnamed libraries; 4.9.0

[srawlins]

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[srawlins]

Should this be 4.9.0-dev? 4.9.0? 4.8.1?

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:code_builder	4.9.0	ready to publish	v4.9.0

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

[devoncarew]

As a new feature, perhaps 4.9.0? You may just want to merge this w/ #439 and rev directly to 4.9.0 (instead of 4.9.0-dev).

[devoncarew]

@srawlins - do you want to update this PR from main (to capture the pubspec + changelog changes from #441_?

[srawlins]

Sorry for the delay. Done.