fix(Dropdown): accessibility - implemented aria-expanded #229

[gselderslaghs]

Proposed changes

Dropdown component missing aria-expanded state, this causes a reduction in exposure to the web accessibility API, see #229

Types of changes

Implemented aria-expanded to initiator, open and close methods

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).

Checklist:

• I have read the CONTRIBUTING document.
• My commit messages follows the conventional commit format
• My change requires a change to the documentation, and updated it accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.