KPropertiesDialog: use the KFileItem when checkig if the url is local

This way we can ge the most local url and urls under e.g. desktop:/ will be detected as local.

This fixes an issue where opening the properties dialog with a file in desktop:/ wouldn't show the group combobox (which allows users to change the group).

BUG: 444624 FIXED-IN: 5.88

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