[Folder View] Don't trash local files

Send the actual URL (e.g. desktop:/foo) to KIO and let it figure it out. Otherwise KDirNotify emits a change for the
backing file:///home/foo/Desktop URL and KDirLister cannot relate the two and doesn't notice a deletion immediately.
Since we don't offer "Move to Trash" for non-local files anyway, this should be safe.

While at it, check for whether files can be moved before offering Trash and whether files can be deleted before
offering Delete (Dolphin does that). I can split that into a separate commit, if you prefer.

CHANGELOG: Fixed long delay when deleting (moving to trash) files on the desktop

Differential Revision: https://phabricator.kde.org/D9914