fix(core/menu-category): allow empty icon as menu-category-item

[jul-lam]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (yarn build) was run locally and any changes were pushed
• Unit tests (yarn test) were run locally and passed
• Visual Regression Tests (yarn visual-regression) were run locally and passed
• Linting (npm lint) was run locally and passed

Pull request type

Please check the type of change your PR introduces:

• Bug fix
• Feature
• Refactoring (no functional changes, no API changes)
• Build related changes
• Documentation content changes
• Other (please describe):

UI changes.

What is the current behavior?

The second level navigation has a default icon defined. Icons on the second level are required. No ellipsis for menu-category.

GitHub Issue Number: N/A

What is the new behavior?

The second level navigation no longer has a default/required icon. Ellipsis for menu-category added.

Does this introduce a breaking change?

• Yes
• No

It is not a breaking change, but the default icon if currently visible is no longer shown.

Testing

Manual tests.

Other information