Add a lisp-data-mode for editing non-code lisp data

Add a lisp-data-mode for editing non-code lisp data

To provide a cleaner implementation remove arguments from the
auxiliary routine lisp-mode-variables.  The modes/functions that need
to do some something special adjustment do them in their own bodies.

* lisp/chistory.el (command-history-mode): Don't pass nil to
lisp-mode-variables.

* lisp/files.el (auto-mode-alist): Add entry for ".dir-locals".

* lisp/help-fns.el (describe-variable): Don't pass useless args to
lisp-mode-variables.

* lisp/emacs-lisp/pp.el (pp-to-string): Don't pass useless args to
lisp-mode-variables.

* lisp/emacs-lisp/lisp-mode.el (lisp-mode-variables):
Simplify.  Always set same variables.
(lisp-data-mode): New major mode.
(lisp-mode): Inherit from lisp-data-mode.  Set special lisp-mode
stuff here.

* lisp/progmodes/elisp-mode.el (emacs-lisp-mode): Inherit from
lisp-data-mode.
(emacs-lisp-mode): Simplify.

* lisp/progmodes/inf-lisp.el (inferior-lisp-mode): Set the needed
syntax table here, not through other function.