Avoid duplicate Edebug symbols when backtracking (Bug#42701)

Avoid duplicate Edebug symbols when backtracking (Bug#42701)

When Edebug backtracks, it nevertheless generates definitions for the
non-matching branches, see Bug#41988 and Bug#42701.  This should be
fixed eventually (probably by deferring the definition until a branch
is known to match), but for now add a band-aid to avoid these
duplicate symbols, at least for anonymous forms.

* lisp/emacs-lisp/edebug.el (edebug-make-enter-wrapper): Regenerate
anonymous names.

* test/lisp/emacs-lisp/edebug-tests.el
(edebug-tests-duplicate-symbol-backtrack): New regression test.