Open a local file.
The file is opened in the current window, or a new window if
`dnd-open-file-other-window' is set. URI is the url for the file,
and must have the format file:file-name or file:///file-name.
The last / in file:/// is part of the file name. If the system
natively supports unc file names, then remote urls of the form
file://server-name/file-name will also be handled by this function.
An alternative for systems that do not support unc file names is
`dnd-open-remote-url'. ACTION is ignored.