Fix visiting zip archives inside tar archives

Fix visiting zip archives inside tar archives

* lisp/tar-mode.el (tar-archive-from-tar): New local variable.
(tar-extract): Set it non-nil for an extracted member that happens
to be arc-mode archive.
* lisp/arc-mode.el (tar-archive-from-tar): Defvar it.
(archive-unique-fname): Make sure FNAME can be created in DIR,
even if FNAME is provided as an absolute file name (this happens
if the archive is a member of a Tar archive, for example).
(archive-extract): Set 'archive-remote' for archives that were
extracted from Tar archives.  (Bug#70987)