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

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.