fix(core/menu-category): fix unwanted behavior with active element

[matthiashader]

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):

What is the current behavior?

Upon reopening the ix-menu, the ix-category appears expanded but contains no items. Only after collapsing and reopening the ix-menu-category, the menu-items become visible again.
Found a small edge case, where the category does not initially open when the menu is expanded

What is the new behavior?

• after menu is collapsed the style of the menuItemContainer is cleared (max-height / opacity)
• changed up the component lifecycle order (in order to initialize the menuExpanded and showItems, which is initially needed in order to show the activeElemement)

Does this introduce a breaking change?

• Yes
• No

Testing

Other information