Improved copy-tree documentation and test (bug#63509)

* etc/NEWS: Move entry since it's an incompatible change.
* lisp/emacs-lisp/shortdoc.el (vector): Make the example relevant.
* lisp/subr.el (copy-tree): Rename second argument,
since 'vector-like' is a term with a specific meaning in Emacs
but not the one intended here.
* doc/lispref/lists.texi (Building Lists): Rename second argument,
and make it clear that the input must be acyclic.
* doc/lispref/records.texi (Record Functions):
Be more precise: `copy-sequence` is used to copy records,
`copy-tree` copies trees made of records etc.
* test/lisp/subr-tests.el (subr--copy-tree): Extend and strengthen the
test considerably, using the print-circle trick to detect structure
sharing precisely.

lisp/emacs-lisp/shortdoc.el

@@ -834,7 +834,7 @@ A FUNC form can have any number of `:no-eval' (or `:no-value'),
    :eval (seq-subseq [1 2 3 4 5] 1 3)
    :eval (seq-subseq [1 2 3 4 5] 1))
   (copy-tree
-   :eval (copy-tree [1 2 3 4]))
+   :eval (copy-tree [1 (2 3) [4 5]] t))
   "Mapping Over Vectors"
   (mapcar
    :eval (mapcar #'identity [1 2 3]))