Don't use parent menu link if disabled

Problem/Motivation

If a menu position rule is attached to a disabled menu link parent, it is still used.
This can be confusing to site builders. It also means users clicking the parent link will get an error page.

Steps to reproduce

Create a new menu position rule and select a menu link as its parent.
Disable the parent menu link.
The breadcrumb still uses the parent.

Proposed resolution

MenuPositionActiveTrail::getActiveLink() could check if the parent is enabled before using it.
However, I am not sure how caching would be handled if the parent is latter re-enabled.

Remaining tasks

• ✅ File an issue
• ➖ Addition/Change/Update/Fix
• ➖ Merge request, Patch, or Commit
• ➖ Testing to ensure no regression
• ➖ Automated unit testing coverage
• ➖ Automated functional testing coverage
• ➖ UX/UI designer responsibilities
• ➖ Readability
• ➖ Accessibility
• ➖ Performance
• ➖ Security
• ➖ Documentation
• ➖ Code review by maintainers
• ➖ Full testing and approval
• ➖ Credit contributors
• ➖ Review with the product owner
• ➖ Release notes snippet
• ❌ Release

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• N/A