Disabled link selected by MenuActiveTrail even though enabled menu item is available

Problem/Motivation

MenuActiveTrail selects the first menu item that is returned by MenuLinkManager::loadLinksByRoute. This results in the menu system potentially selecting a disabled menu item, even if an enabled item is available in the menu, but comes later in the link list.
Therefore, a path that does have an active menu item may not be presented to the user in the menu at all, as the disabled item was picked by the system.

Steps to reproduce

1. Create two menu items to the same path or content
2. Assign them increasing weights
3. Disable the first item.
4. Navigate to the linked path or content

Result: The first menu item will be picked.

Expected behavior

As an active menu item is available, the first such link (2nd link in our example) will be set active.

Proposed resolution

Adjust MenuActiveTrail::getActiveLink to check the enabled state of the menu links with a fallback.