New user option 'debugger-stack-frame-as-list'

New user option 'debugger-stack-frame-as-list'

* src/eval.c (syms_of_eval) <debugger-stack-frame-as-list>: New
variable.
* lisp/cus-start.el (standard): Add debugger-stack-frame-as-list.
* lisp/emacs-lisp/debug.el (debugger-setup-buffer): Adjust
backtrace processing for the value of debugger-stack-frame-as-list.
* lisp/emacs-lisp/edebug.el (edebug-backtrace): Adjust backtrace
processing for the value of debugger-stack-frame-as-list.
* doc/lispref/debugging.texi (Internals of Debugger): Document
debugger-stack-frame-as-list.
* etc/NEWS: Mention 'debugger-stack-frame-as-list'.