New macros incf and decf

New macros incf and decf

* lisp/emacs-lisp/cl-lib.el (cl-incf, cl-decf): Move macros from here...
* lisp/emacs-lisp/gv.el (incf, decf): ...to here.  Make old names into
aliases, documented as deprecated.
* lisp/obsolete/cl.el: Don't alias incf and decf.

* test/lisp/emacs-lisp/cl-lib-tests.el (cl-lib-test-incf)
(cl-lib-test-decf): Move tests from here...
* test/lisp/emacs-lisp/gv-tests.el (gv-incf, gv-decf): ...to here.

* doc/lispref/numbers.texi (Arithmetic Operations):
* lisp/emacs-lisp/shortdoc.el (number): Document incf and decf.

* doc/lispref/variables.texi (Multisession Variables):
* doc/misc/cl.texi (Organization, Modify Macros, Modify Macros)
(Modify Macros, Macro Bindings, For Clauses, Property Lists)
(Structures, Efficiency Concerns, Obsolete Setf Customization): Delete
cl-incf and cl-decf documentation, moving any relevant parts to lispref.
Delete some parts that seem to primarily regard implementation details
that do not warrant inclusion in lispref.  Update all examples to use
incf/decf.

(cherry picked from commit 95fee880e45184f4820e9704b75887ef2d91bd01)