Support ellipsis expansion in cl-print

Support ellipsis expansion in cl-print

* lisp/emacs-lisp/cl-print.el (cl-print-object-contents): New
generic method.
(cl-print-object-contents) <cons, vector,cl-structure-object>: New
methods.
(cl-print-object) <cons>: Use cl-print-insert-ellipsis.
(cl-print-object) <vector, cl-structure-object>: Elide whole object if
print-level exceeded.  Use cl-print-insert-ellipsis.
(cl-print-insert-ellipsis, cl-print-propertize-ellipsis)
(cl-print-expand-ellipsis): New functions.

* test/lisp/emacs-lisp/cl-print-tests.el (cl-print-tests-4): Test
printing of objects nested in other objects.
(cl-print-tests-strings, cl-print-tests-ellipsis-cons)
(cl-print-tests-ellipsis-vector, cl-print-tests-ellipsis-struct)
(cl-print-tests-ellipsis-circular): New tests.
(cl-print-tests-check-ellipsis-expansion)
(cl-print-tests-check-ellipsis-expansion-rx): New functions.