remove fixup component for <Link><Menu.Item/></Link>

[yyxcv]

In App.tsx there are two "fixup components" that could be removed (MenuItemForLink and DropDownItemForLink).

These were introduced because a warning is shown if we put an \ in a \:

The problem is only triggered (and not caused) by the \ \ nesting. It is caused by the <>-element in the \ in App.tsx (As suggested here https://stackoverflow.com/questions/66463284/react-router-warning-route-elements-should-not-change-from-controlled-to-unco).

This pr:

• Removes the "fixup components" (MenuItemForLink and DropDownItemForLink)
• replaces them with Menu.Item and Dropdown.Item
• puts the conditionally added routes in \ in an array instead of an <>-element
• gets rid of the warning

Benefit:

• the fixup components caused some type errors on their props. these are gone now.
• better clarity and readabiltiy

[gluap]

Thank you for investigating this so thoroughly. We've merged a large number of changes from the next branch.

Could you rebase this onto main to make it merge? We'd gladly release it with the next version!

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

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0.0% Duplication

[opatut]

I finally got around to cherry picking this onto the current next branch. There were some CSS issues after the component restructure, which I fixed. You're still mentioned as author @yyxcv on the commit, but I couldn't push to your MR branch, so I have to close this without merging. The code is in though, thanks for your contribution.