[WidgetFactory] Move isLocalFile() check, toLocalFile() to setters
Summary:
Avoid converting the KFileItem to a path for the common case of only
showing the file attributes.
This is the first/preparatory part.
Reviewers: Baloo, astippich, ngraham
Reviewed By: astippich
Tags: Baloo
Differential Revision: https://phabricator.kde.org/D20979