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/eval.h

@@ -167,6 +167,7 @@ typedef enum {
   VV_COLLATE,
   VV_EXITING,
   VV_MAXCOL,
+  VV_STACKTRACE,
   // Nvim
   VV_STDERR,
   VV_MSGPACK_TYPES,