DropdownMenu composition

[mwarman]

📢 Instructions

• Begin with a DRAFT pull request.
• Follow italicized instructions to add detail to assist the reviewers.
• After completing all checklist items, change the pull request to READY.

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🔧 Change Summary

Describe the changes included in this pull request. Link to the associated GitHub issue(s).

• fixes Dropdown composition #5
• Added the DropdownMenu component which replaces the Dropdown component.
• DropdownMenu uses the compound pattern and emphasizes composition to create menu content.

📝 Checklist

Pull request authors must complete the following tasks before marking the PR as ready to review.

• Complete a self-review of changes
• Unit tests have been created or updated
• The code is free of [new] lint errors and warnings
• Update storybook stories as needed
• Update project documentation as needed, README, JSDoc, etc.

🧪 Steps to Test

Describe the process to test the changes in this pull request.

The DropdownMenu may be viewed in Storybook. There are some quirks in how Storybook renders the component inside of the preview panel due to the Backdrop component used by DropdownMenu using fixed positioning.

Within the app, these changes may be tested by...

1. Click the Language Toggle button in the header of the application.
2. The language toggle is the example of a DropdownMenu implementation within the app.

🔗 Additional Information

Optionally, provide additional details, screenshots, or URLs that may assist the reviewer.

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