vim-patch:9.1.0984: exception handling can be improved

Problem:  exception handling can be improved
Solution: add v:stacktrace and getstacktrace()

closes: vim/vim#16360

663d18d610

Co-authored-by: ichizok <gclient.gaap@gmail.com>
Co-authored-by: Naruhiko Nishino <naru123456789@gmail.com>

src/nvim/ex_eval_defs.h

@@ -2,6 +2,7 @@
 
 #include <stdbool.h>
 
+#include "nvim/eval/typval_defs.h"
 #include "nvim/pos_defs.h"
 
 /// A list used for saving values of "emsg_silent".  Used by ex_try() to save the
@@ -107,6 +108,7 @@ struct vim_exception {
   msglist_T *messages;  ///< message(s) causing error exception
   char *throw_name;     ///< name of the throw point
   linenr_T throw_lnum;  ///< line number of the throw point
+  list_T *stacktrace;   ///< stacktrace
   except_T *caught;     ///< next exception on the caught stack
 };