vim-patch:8.1.0105: all tab stops are the same

Problem:    All tab stops are the same.
Solution:   Add the variable tabstop feature. (Christian Brabandt,
            closes vim/vim#2711)
04958cbaf2

src/nvim/eval/funcs.c

@@ -4312,6 +4312,7 @@ static void f_has(typval_T *argvars, typval_T *rettv, FunPtr fptr)
     "title",
     "user-commands",        // was accidentally included in 5.4
     "user_commands",
+    "vartabs",
     "vertsplit",
     "virtualedit",
     "visual",