vim-patch:8.2.4359: crash when repeatedly using :retab

Problem:    crash when repeatedly using :retab.
Solution:   Bail out when the line is getting too long.
6e28703a8e

Cherry-pick e_resulting_text_too_long from v8.2.3492; put it in globals.h as
it will eventually be used in other files.

Add a modeline to test_retab.vim

src/nvim/ex_cmds.c

@@ -847,6 +847,10 @@ void ex_retab(exarg_T *eap)
         break;
       }
       vcol += win_chartabsize(curwin, ptr + col, (colnr_T)vcol);
+      if (vcol >= MAXCOL) {
+        emsg(_(e_resulting_text_too_long));
+        break;
+      }
       col += utfc_ptr2len(ptr + col);
     }
     if (new_line == NULL) {                 // out of memory