[Annotation plugin] Avoid adding same image multi times

[Chaoba]

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Fixes: #71

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.
• Apply changelog label ('breaking change', 'bug 🪲', 'build', 'docs', 'feature 🍏', 'performance ⚡', 'testing 💯') or use the label 'skip changelog'
• Add an entry inside this element for inclusion in the mapbox-maps-android changelog: <changelog>[Annotation plugin] Avoid adding same image multi times</changelog>.

Summary of changes

The same bitmap could be added to style for multi times if multi symbols use this bitmap.
This PR adds the check to avoid adding the same image multi times.

User impact (optional)