Add new commands to Edebug backtraces

Add new commands to Edebug backtraces

Add commands to go to source if available, and to show and hide
Edebug's instrumentation.  Make Edebug pop to backtraces instead of
displaying them, which makes Edebug consistant with the behavior of
ERT and the Lisp Debugger.
* doc/lispref/edebug.texi (Edebug Misc): Document when and how you can
jump to source code from an Edebug backtrace.  Document
'edebug-backtrace-show-instrumentation' and
'edebug-backtrace-hide-instrumentation'.
* lisp/emacs-lisp/backtrace.el (backtrace-frame): Add comments to
describe the fields.
(backtrace-goto-source-functions): New
abnormal hook.
(backtrace-mode-map): Add keybinding and menu item for
backtrace-goto-source.
(backtrace--flags-width): New constant.
(backtrace-update-flags): Use it.
(backtrace-goto-source): New command.
(backtrace--print-flags): Print the :source-available flag.
* lisp/emacs-lisp/edebug.el (edebug-backtrace-frames)
(edebug-instrumented-backtrace-frames): New variables.
(edebug-backtrace, edebug--backtrace-frames): Remove functions.
(edebug-pop-to-backtrace, edebug--backtrace-goto-source)
(edebug--add-source-info): New functions.
(edebug-mode-map, edebug-mode-menus): Replace 'edebug-backtrace' with
'edebug-pop-to-backtrace'.
(edebug--strip-instrumentation): New function.
(edebug--unwrap-and-add-info): Remove.
(edebug-unwrap-frame, edebug-add-source-info): New functions.
(edebug-backtrace-show-instrumentation)
(edebug-backtrace-hide-instrumentation): New commands.
* test/lisp/emacs-lisp/edebug-tests.el (edebug-tests-check-keymap):
Verify keybindings in backtrace-mode-map used by new test.
Update with binding for 'edebug-pop-to-backtrace'.
(edebug-tests-backtrace-goto-source): New test.
* test/lisp/emacs-lisp/edebug-resources/edebug-test-code.el
(edebug-test-code-range): Add a new stop point.