BUGFIX: Neos.Neos Fusion ErrorCase wrongly included

[mhsdesign]

Fixes: #4035

#3915 introduced a regression, that the errorCase was not included at all. With #3996 this was hotfixed but lead to another regression that i am here to fix.

If we include Neos.Neos/Resources/Private/Fusion/Error/Root.fusion we also re include include: resource://Neos.Fusion/Private/Fusion/Root.fusion which is not optimal.

The errorCase is now (again) on its own and doesnt belong to the Error folder anymore but like the RootCase, sits on top.

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• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
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