[Annotation plugin] Change annotations from map to list

[Chaoba]

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Fixes: < Link to related issues that will be fixed by this pull request, if they exist >

Pull request checklist:

• Briefly describe the changes in this PR.
• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality. If tests were not written, please explain why.
• Add example if relevant.
• Document any changes to public APIs.
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• Add an entry inside this element for inclusion in the mapbox-maps-android changelog: <changelog>[Annotation plugin] Change annotations from map to list</changelog>.

Summary of changes

The type of annotations in AnnotationManger is Map, which is not convenient for users. This pr change its type from Map to List.

User impact (optional)